Having the same or at least similar issue on a DELL XPS13 (9360) D600 Dock. The thunderbolt connection suddenly drops for a few seconds and the automatically reconnects again. Screens go blank for that time and all peripherals also gets disconnected. This happens randomly but at least twice an hour. All firmware is up-to-date.

OS: Ubuntu 20.04 LTS (5.4.0-40-generic)
Hardware: DELL XPS 13 (9360); Intel Core i7-7500U CPU, 8GB RAM
Dock: DELL D600 (with two 1080p monitors connected over DisplayPort)

Here the dmesg:
[ 4088.809311] show_signal_msg: 3032 callbacks suppressed
[ 4088.809314] ActiveCommandQu[6618]: segfault at 7f244c19f000 ip 0000000000998e9e sp 00007f244e7fa438 error 4 in DisplayLinkManager[400000+937000]
[ 4088.809321] Code: 3d db fb c4 c1 3d 72 d0 08 c4 e3 fd 00 d7 d8 c5 bd db fb c5 6d f9 d8 c5 ed fd d0 c5 ed fd d0 c5 ed fd c9 c5 fd 6f 17 4c 01 cf <c5> 7d 6f 17 c5 f5 71 d1 02 c5 ed db c3 c5 ed 72 d2 08 c5 7d 6f 24
[ 4093.927731] evdi: [D] evdi_driver_postclose:133 (dev=2) Process tries to close us, postclose
[ 4093.927733] evdi: [I] Task 1148 (DesktopManagerE) of process 1139 (DisplayLinkMana)
[ 4093.927736] evdi: [D] evdi_painter_disconnect:817 (dev=2) Disconnected from 000000009024a4f0
[ 4093.927739] evdi: [D] evdi_detect:94 (dev=-1) poll connector state: disconnected
[ 4093.927788] evdi: [D] evdi_driver_postclose:133 (dev=1) Process tries to close us, postclose
[ 4093.927789] evdi: [I] Task 1148 (DesktopManagerE) of process 1139 (DisplayLinkMana)
[ 4093.927791] evdi: [D] evdi_painter_disconnect:817 (dev=1) Disconnected from 00000000a19585cf
[ 4093.927792] evdi: [D] evdi_detect:94 (dev=-1) poll connector state: disconnected
[ 4094.278010] evdi: [D] evdi_detect:94 (dev=-1) poll connector state: disconnected
[ 4094.278026] evdi: [D] evdi_detect:94 (dev=-1) poll connector state: disconnected
[ 4094.278039] evdi: [D] evdi_detect:94 (dev=-1) poll connector state: disconnected
[ 4094.278048] evdi: [D] evdi_detect:94 (dev=-1) poll connector state: disconnected
[ 4094.278058] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4094.278064] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4094.278072] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4094.278078] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4094.278514] evdi: [D] evdi_painter_dpms_notify:654 (dev=-1) Notifying dpms mode: 3
[ 4094.278515] evdi: [W] evdi_painter_send_event:307 Painter is not connected!
[ 4094.597176] evdi: [D] evdi_detect:94 (dev=-1) poll connector state: disconnected
[ 4094.597190] evdi: [D] evdi_detect:94 (dev=-1) poll connector state: disconnected
[ 4094.597202] evdi: [D] evdi_detect:94 (dev=-1) poll connector state: disconnected
[ 4094.597210] evdi: [D] evdi_detect:94 (dev=-1) poll connector state: disconnected
[ 4094.597220] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4094.597227] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4094.597237] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4094.597245] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4094.761411] evdi: [D] evdi_painter_dpms_notify:654 (dev=-1) Notifying dpms mode: 3
[ 4094.761413] evdi: [W] evdi_painter_send_event:307 Painter is not connected!
[ 4095.603371] evdi: [D] evdi_painter_dpms_notify:654 (dev=0) Notifying dpms mode: 3
[ 4095.603373] evdi: [W] evdi_painter_send_event:307 Painter is not connected!
[ 4095.603384] evdi: [D] evdi_painter_dpms_notify:654 (dev=0) Notifying dpms mode: 3
[ 4095.603385] evdi: [W] evdi_painter_send_event:307 Painter is not connected!
[ 4095.603397] evdi: [D] evdi_painter_dpms_notify:654 (dev=-1) Notifying dpms mode: 3
[ 4095.603398] evdi: [W] evdi_painter_send_event:307 Painter is not connected!
[ 4095.603478] evdi: [D] evdi_painter_dpms_notify:654 (dev=-1) Notifying dpms mode: 3
[ 4095.603479] evdi: [W] evdi_painter_send_event:307 Painter is not connected!
[ 4099.415992] evdi: [D] evdi_painter_connect:738 (dev=-1) Process is trying to connect
[ 4099.415994] evdi: [I] Task 6702 (DesktopManagerE) of process 6696 (DisplayLinkMana)
[ 4099.415997] evdi: [D] evdi_painter_connect:788 (dev=1) Connected with 00000000e47f4312
[ 4099.416000] evdi: [D] evdi_detect:90 (dev=1) poll connector state: connected
[ 4099.423785] evdi: [D] evdi_painter_connect:738 (dev=-1) Process is trying to connect
[ 4099.423787] evdi: [I] Task 6702 (DesktopManagerE) of process 6696 (DisplayLinkMana)
[ 4099.423790] evdi: [D] evdi_painter_connect:788 (dev=2) Connected with 00000000040a913a
[ 4099.423792] evdi: [D] evdi_detect:90 (dev=2) poll connector state: connected
[ 4099.430545] evdi: [D] evdi_detect:90 (dev=1) poll connector state: connected
[ 4099.430547] evdi: [D] evdi_painter_get_edid_copy:228 (dev=1) EDID valid
[ 4099.430701] evdi: [D] evdi_detect:90 (dev=1) poll connector state: connected
[ 4099.430702] evdi: [D] evdi_painter_get_edid_copy:228 (dev=1) EDID valid
[ 4099.430871] evdi: [D] evdi_detect:90 (dev=2) poll connector state: connected
[ 4099.430873] evdi: [D] evdi_painter_get_edid_copy:228 (dev=2) EDID valid
[ 4099.431016] evdi: [D] evdi_detect:90 (dev=2) poll connector state: connected
[ 4099.431017] evdi: [D] evdi_painter_get_edid_copy:228 (dev=2) EDID valid
[ 4099.431188] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4099.431196] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4099.431205] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4099.431212] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4099.624388] evdi: [D] evdi_detect:90 (dev=1) poll connector state: connected
[ 4099.624392] evdi: [D] evdi_painter_get_edid_copy:228 (dev=1) EDID valid
[ 4099.624566] evdi: [D] evdi_detect:90 (dev=1) poll connector state: connected
[ 4099.624568] evdi: [D] evdi_painter_get_edid_copy:228 (dev=1) EDID valid
[ 4099.624778] evdi: [D] evdi_detect:90 (dev=2) poll connector state: connected
[ 4099.624781] evdi: [D] evdi_painter_get_edid_copy:228 (dev=2) EDID valid
[ 4099.624916] evdi: [D] evdi_detect:90 (dev=2) poll connector state: connected
[ 4099.624917] evdi: [D] evdi_painter_get_edid_copy:228 (dev=2) EDID valid
[ 4099.625074] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4099.625082] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4099.625091] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4099.625096] evdi: [D] evdi_detect:94 (dev=0) poll connector state: disconnected
[ 4100.485886] evdi: [D] evdi_painter_dpms_notify:654 (dev=2) Notifying dpms mode: 0
[ 4100.485904] evdi: [D] evdi_painter_mode_changed_notify:701 (dev=2) Notifying mode changed: 1920x1080@60; bpp 32; 
[ 4100.485905] evdi: [D] evdi_log_pixel_format:680 pixel format XR24 little-endian (0x34325258)
[ 4100.485906] evdi: [D] evdi_painter_dpms_notify:654 (dev=2) Notifying dpms mode: 0
[ 4100.514438] evdi: [D] evdi_painter_dpms_notify:654 (dev=1) Notifying dpms mode: 0
[ 4100.514465] evdi: [D] evdi_painter_mode_changed_notify:701 (dev=1) Notifying mode changed: 1920x1080@60; bpp 32; 
[ 4100.514468] evdi: [D] evdi_log_pixel_format:680 pixel format XR24 little-endian (0x34325258)
[ 4100.514470] evdi: [D] evdi_painter_dpms_notify:654 (dev=1) Notifying dpms mode: 0
[ 4100.515878] evdi: [D] evdi_painter_dpms_notify:654 (dev=0) Notifying dpms mode: 3
[ 4100.515884] evdi: [W] evdi_painter_send_event:307 Painter is not connected!
[ 4100.515915] evdi: [D] evdi_painter_dpms_notify:654 (dev=0) Notifying dpms mode: 3
[ 4100.515916] evdi: [W] evdi_painter_send_event:307 Painter is not connected!
[ 4117.118079] Lockdown: systemd-logind: hibernation is restricted; see man kernel_lockdown.7