As requested by a maintainer of FFADE, the output of the diagnose tool. This is most likely to do with device rights for the user or group.

UPDATE: When I looked at the output of the diagnose tool, I see two Firewire devices with different user/group rights. (The card in the desktop has actually three places to add a FireWire cable, not two.) When I plug in on the left connector, this user rights issue occurs. But when I plug it into the middle, the issue is gone. 

So this might nog be an issue for FFADO. I have another desktop with FireWire and a DV camera. I notived also that the port I use there has influence in how I can connect to the camera. Will test this later on and add the findings here. Perhaps there is a convention or default config to offer FireWire #0 only for root and #1 also for group audio?

obs@obs:~$ ffado-diag 
FFADO diagnostic utility 2.4.4

(C) 2008 Pieter Palmers
    2009-2010 Arnold Krille
    2018 Nicolas Boulenguez, Jonathan Woithe

gcc                       /usr/bin/gcc
                          gcc (Ubuntu 10.3.0-1ubuntu1) 10.3.0
g++                       /usr/bin/g++
                          g++ (Ubuntu 10.3.0-1ubuntu1) 10.3.0
pyuic4                    None
pyuic5                    None
jackd                     None
pkg-config                /usr/bin/pkg-config
jack                      1.9.17
                          -ljack
libraw1394                2.1.2
                          -lraw1394
libavc1394                not found
libiec61883               not found
libxml++-2.6              not found
dbus-1                    1.12.20
                          -I/usr/include/dbus-1.0 -I/usr/lib/x86_64-linux-gnu/dbus-1.0/include -ldbus-1

Build time info           /usr/lib/x86_64-linux-gnu/libffado/static_info.txt
  gcc                       /usr/bin/gcc
                            gcc (Ubuntu 10.2.1-6ubuntu2) 10.2.1 20210121
  g++                       /usr/bin/g++
                            g++ (Ubuntu 10.2.1-6ubuntu2) 10.2.1 20210121
  pyuic4                    None
  pyuic5                    /usr/bin/pyuic5
                            Python User Interface Compiler 5.15.2 for Qt version 5.15.2
  jackd                     None
  pkg-config                /usr/bin/pkg-config
  jack                      not found
  libraw1394                2.1.2
                            -lraw1394
  libavc1394                not found
  libiec61883               1.2.0
                            -liec61883 -lraw1394
  libxml++-2.6              2.40.1
                            -I/usr/include/libxml++-2.6 -I/usr/lib/x86_64-linux-gnu/libxml++-2.6/include -I/usr/include/libxml2 -I/usr/include/glibmm-2.4 -I/usr/lib/x86_64-linux-gnu/glibmm-2.4/include -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/sigc++-2.0 -I/usr/lib/x86_64-linux-gnu/sigc++-2.0/include -lxml++-2.6 -lxml2 -lglibmm-2.4 -lgobject-2.0 -lglib-2.0 -lsigc-2.0
  dbus-1                    1.12.20
                            -I/usr/include/dbus-1.0 -I/usr/lib/x86_64-linux-gnu/dbus-1.0/include -ldbus-1

kernel version            5.11.0-7614-generic
Preempt (low latency)     False
RT patched                False
/dev/fw*                  ['/dev/fw1', '/dev/fw0']
  crw-------  1 root root  241, 0 May 10 10:44 /dev/fw0
  crw-rw----+ 1 root audio 241, 1 May 10 10:47 /dev/fw1
User IDs                  uid=1000(obs) gid=1000(obs) groups=1000(obs),27(sudo)
uname -a                  Linux obs 5.11.0-7614-generic #15~1618626693~21.04~ecb25cd-Ubuntu SMP Thu Apr 22 15:59:53 UTC  x86_64 x86_64 x86_64 GNU/Linux
lspci                     /usr/bin/lspci
  05:06.0 FireWire (IEEE 1394) [0c00]: VIA Technologies, Inc. VT6306/7/8 [Fire II(M)] IEEE 1394 OHCI Controller [1106:3044] (rev 46) (prog-if 10 [OHCI])
  	Subsystem: VIA Technologies, Inc. VT6306/7/8 [Fire II(M)] IEEE 1394 OHCI Controller [1106:3044]
  	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping+ SERR- FastB2B- DisINTx-
  	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
  	Latency: 32 (8000ns max), Cache Line Size: 64 bytes
  	Interrupt: pin A routed to IRQ 21
  	NUMA node: 0
  	Region 0: Memory at fe100000 (32-bit, non-prefetchable) [size=2K]
  	Region 1: I/O ports at b000 [size=128]
  	Capabilities: <access denied>
  	Kernel driver in use: firewire_ohci
  	Kernel modules: firewire_ohci
lscpu                     /usr/bin/lscpu
  Architecture:                    x86_64
  CPU op-mode(s):                  32-bit, 64-bit
  Byte Order:                      Little Endian
  Address sizes:                   48 bits physical, 48 bits virtual
  CPU(s):                          6
  On-line CPU(s) list:             0-5
  Thread(s) per core:              2
  Core(s) per socket:              3
  Socket(s):                       1
  NUMA node(s):                    1
  Vendor ID:                       AuthenticAMD
  CPU family:                      21
  Model:                           1
  Model name:                      AMD FX(tm)-6100 Six-Core Processor
  Stepping:                        2
  Frequency boost:                 enabled
  CPU MHz:                         1428.966
  CPU max MHz:                     3300.0000
  CPU min MHz:                     1400.0000
  BogoMIPS:                        6628.93
  Virtualization:                  AMD-V
  L1d cache:                       48 KiB
  L1i cache:                       192 KiB
  L2 cache:                        6 MiB
  L3 cache:                        8 MiB
  NUMA node0 CPU(s):               0-5
  Vulnerability Itlb multihit:     Not affected
  Vulnerability L1tf:              Not affected
  Vulnerability Mds:               Not affected
  Vulnerability Meltdown:          Not affected
  Vulnerability Spec store bypass: Mitigation; Speculative Store Bypass disabled via prctl and seccomp
  Vulnerability Spectre v1:        Mitigation; usercopy/swapgs barriers and __user pointer sanitization
  Vulnerability Spectre v2:        Mitigation; Full AMD retpoline, IBPB conditional, STIBP disabled, RSB filling
  Vulnerability Srbds:             Not affected
  Vulnerability Tsx async abort:   Not affected
  Flags:                           fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc cpuid extd_apicid aperfmperf pni pclmulqdq monitor ssse3 cx16 sse4_1 sse4_2 popcnt aes xsave avx lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs xop skinit wdt fma4 nodeid_msr topoext perfctr_core perfctr_nb cpb hw_pstate ssbd ibpb vmmcall arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold

Hardware interrupts
  IRQ   0 PID      count      34,0,0,0,0,0 Sched     priority     drivers IO-APIC,2-edge,timer
  IRQ   8 PID      count       0,0,0,0,1,0 Sched     priority     drivers IO-APIC,8-edge,rtc0
  IRQ   9 PID      count       0,0,0,0,0,0 Sched     priority     drivers IO-APIC,9-fasteoi,acpi
  IRQ  14 PID      count       0,0,0,0,0,0 Sched     priority     drivers IO-APIC,14-edge,pata_atiixp
  IRQ  15 PID      count       0,0,0,0,0,0 Sched     priority     drivers IO-APIC,15-edge,pata_atiixp
  IRQ  16 PID      count 0,0,2089,0,3628,0 Sched     priority     drivers IO-APIC,16-fasteoi,ohci_hcd:usb3,,ohci_hcd:usb4,,snd_hda_intel:card0
  IRQ  17 PID      count       2,0,0,0,0,0 Sched     priority     drivers IO-APIC,17-fasteoi,ehci_hcd:usb1
  IRQ  18 PID      count       0,0,0,3,0,0 Sched     priority     drivers IO-APIC,18-fasteoi,ohci_hcd:usb5,,ohci_hcd:usb6,,ohci_hcd:usb7
  IRQ  19 PID      count    0,1479,0,0,0,0 Sched     priority     drivers IO-APIC,19-fasteoi,ehci_hcd:usb2,,snd_hda_intel:card1
  IRQ  21 PID      count   0,0,0,3,65360,0 Sched     priority     drivers IO-APIC,21-fasteoi,firewire_ohci
  IRQ  22 PID      count     0,9,457,0,0,0 Sched     priority     drivers IO-APIC,22-fasteoi,ahci[0000:00:11.0]
  IRQ  28 PID      count       0,0,0,0,0,0 Sched     priority     drivers PCI-MSI,1572864-edge,xhci_hcd
  IRQ  29 PID      count       0,0,0,0,0,0 Sched     priority     drivers PCI-MSI,1572865-edge,xhci_hcd
  IRQ  30 PID      count       0,0,0,0,0,0 Sched     priority     drivers PCI-MSI,1572866-edge,xhci_hcd
  IRQ  31 PID      count       0,0,0,0,0,0 Sched     priority     drivers PCI-MSI,1572867-edge,xhci_hcd
  IRQ  32 PID      count       0,0,0,0,0,0 Sched     priority     drivers PCI-MSI,1572868-edge,xhci_hcd
  IRQ  33 PID      count       0,0,0,0,0,0 Sched     priority     drivers PCI-MSI,1572869-edge,xhci_hcd
  IRQ  34 PID      count       0,0,0,0,0,0 Sched     priority     drivers PCI-MSI,1572870-edge,xhci_hcd
  IRQ  35 PID      count0,0,22020,0,15085,0 Sched     priority     drivers PCI-MSI,1048576-edge,ahci[0000:02:00.0]
  IRQ  36 PID      count0,0,0,132411,0,1187 Sched     priority     drivers PCI-MSI,524288-edge,nvidia
  IRQ  37 PID      count1526,0,0,0,0,130869 Sched     priority     drivers PCI-MSI,2097152-edge,enp4s0

Software interrupts

module directory          /lib/modules/5.11.0-7614-generic
Old 1394 stack
  ieee1394 not present
  ieee1394 not loaded
  ohci1394 not present
  ohci1394 not loaded
  raw1394 not present
  raw1394 not loaded
stack active              False
statically linked         False
New 1394 stack
  firewire-core present
  firewire-core loaded
  firewire-ohci present
  firewire-ohci loaded
stack active              True
statically linked         False
Kernel support:
  The new FireWire kernel stack is loaded.
  If running a kernel earlier than 2.6.37 and problems are experienced, either
  try with the old Firewire kernel stack or upgrade to a newer kernel
  (preferrably 2.6.37 or later).