Description of problem:
Try to detect my network printer HP Photosmart C8260 using the command :
 % hp-probe -bnet -ldebug

Output of the command :

HP Linux Imaging and Printing System (ver. 3.18.4)
Printer Discovery Utility ver. 4.1

Copyright (c) 2001-15 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.


--------------------
| DEVICE DISCOVERY |
--------------------

Probing network for printers. Please wait, this will take approx. 10 seconds...

hp-probe[1859]: debug: {}
hp-probe[1859]: debug: 0000:  01 07 01 a7 00 00 65 6e 00 03 00 00 00 00 01 97 28 78 2d 68 70 2d 76 65 72 3d 30 31 29 28 78 2d  ......en........(x-hp-ver=01)(x-
hp-probe[1859]: debug: 0020:  68 70 2d 6d 61 63 3d 30 30 31 65 30 62 39 61 35 63 63 63 29 28 78 2d 68 70 2d 6e 75 6d 5f 70 6f  hp-mac=001e0b9a5ccc)(x-hp-num_po
hp-probe[1859]: debug: 0040:  72 74 3d 30 31 29 28 78 2d 68 70 2d 69 70 3d 31 39 32 2e 31 36 38 2e 32 34 36 2e 30 31 31 29 28  rt=01)(x-hp-ip=192.168.246.011)(
hp-probe[1859]: debug: 0060:  78 2d 68 70 2d 68 6e 3d 48 50 39 41 35 43 43 43 29 28 78 2d 68 70 2d 70 31 3d 4d 46 47 3a 48 50  x-hp-hn=HP9A5CCC)(x-hp-p1=MFG:HP
hp-probe[1859]: debug: 0080:  3b 4d 44 4c 3a 50 68 6f 74 6f 73 6d 61 72 74 20 43 36 32 30 30 20 73 65 72 69 65 73 3b 43 4d 44  ;MDL:Photosmart C6200 series;CMD
hp-probe[1859]: debug: 00a0:  3a 4d 4c 43 2c 50 43 4c 2c 50 4d 4c 2c 44 57 2d 50 43 4c 2c 44 45 53 4b 4a 45 54 2c 44 59 4e 3b  :MLC,PCL,PML,DW-PCL,DESKJET,DYN;
hp-probe[1859]: debug: 00c0:  31 32 38 34 2e 34 44 4c 3a 34 64 2c 34 65 2c 31 3b 43 4c 53 3a 50 52 49 4e 54 45 52 3b 44 45 53  1284.4DL:4d,4e,1;CLS:PRINTER;DES
hp-probe[1859]: debug: 00e0:  3a 43 43 39 38 38 3b 53 4e 3a 4d 59 37 43 49 48 35 31 30 50 30 35 30 36 3b 53 3a 30 33 38 30 38  :CC988;SN:MY7CIH510P0506;S:03808
hp-probe[1859]: debug: 0100:  38 43 34 38 34 30 30 31 30 32 31 30 30 37 38 63 62 30 30 30 30 30 34 31 62 38 30 34 32 37 34 36  8C4840010210078cb0000041b8042746
hp-probe[1859]: debug: 0120:  62 38 30 34 34 38 34 37 62 38 30 34 34 65 34 34 62 38 30 34 36 34 34 38 62 38 30 30 35 35 34 35  b8044847b8044e44b8046448b8005545
hp-probe[1859]: debug: 0140:  62 38 30 34 36 34 3b 5a 3a 30 31 30 32 2c 30 35 30 30 30 30 30 39 30 31 36 61 38 35 30 31 33 32  b80464;Z:0102,05000009016a850132
hp-probe[1859]: debug: 0160:  34 35 30 31 33 32 34 35 30 31 33 32 34 35 30 31 33 32 34 31 30 31 33 32 34 35 21 73 54 f0 a0 29  45013245013245013241013245!sT..)
hp-probe[1859]: debug: 0180:  4d 7d 21 73 55 ac ff ff fa 40 a0 39 c7 3f 29 28 78 2d 68 70 2d 67 75 69 64 3d 30 30 31 65 30 62  M}!sU....@.9.?)(x-hp-guid=001e0b
hp-probe[1859]: debug: 01a0:  39 61 35 63 63 63 29                                                                             9a5ccc)
Traceback (most recent call last):
  File "/usr/bin/hp-probe", line 162, in <module>
    devices = device.probeDevices([b], timeout, ttl, filter_dict, search, method)
  File "/usr/share/hplip/base/device.py", line 487, in probeDevices
    detected_devices = slp.detectNetworkDevices(ttl, timeout)
  File "/usr/share/hplip/base/slp.py", line 115, in detectNetworkDevices
    x= to_string_utf8(x)
  File "/usr/share/hplip/base/sixext.py", line 113, in to_string_utf8
    return s.decode("utf-8")
UnicodeDecodeError: 'utf-8' codec can't decode bytes in position 365-366: invalid continuation byte

Version-Release number of selected component:
hplip-3.18.4-1.fc28

Additional info:
reporter:       libreport-2.9.5
cmdline:        /usr/bin/python3 /usr/bin/hp-probe -bnet -ldebug
crash_function: to_string_utf8
exception_type: UnicodeDecodeError
executable:     /usr/bin/hp-probe
interpreter:    python3-3.6.5-1.fc28.x86_64
kernel:         4.16.5-300.fc28.x86_64
runlevel:       N 5
type:           Python3
uid:            1000

Truncated backtrace:
sixext.py:113:to_string_utf8:UnicodeDecodeError: 'utf-8' codec can't decode bytes in position 365-366: invalid continuation byte

Traceback (most recent call last):
  File "/usr/bin/hp-probe", line 162, in <module>
    devices = device.probeDevices([b], timeout, ttl, filter_dict, search, method)
  File "/usr/share/hplip/base/device.py", line 487, in probeDevices
    detected_devices = slp.detectNetworkDevices(ttl, timeout)
  File "/usr/share/hplip/base/slp.py", line 115, in detectNetworkDevices
    x= to_string_utf8(x)
  File "/usr/share/hplip/base/sixext.py", line 113, in to_string_utf8
    return s.decode("utf-8")
UnicodeDecodeError: 'utf-8' codec can't decode bytes in position 365-366: invalid continuation byte

Local variables in innermost frame:
s: b'(x-hp-ver=01)(x-hp-mac=001e0b9a5ccc)(x-hp-num_port=01)(x-hp-ip=192.168.246.011)(x-hp-hn=HP9A5CCC)(x-hp-p1=MFG:HP;MDL:Photosmart C6200 series;CMD:MLC,PCL,PML,DW-PCL,DESKJET,DYN;1284.4DL:4d,4e,1;CLS:PRINTER;DES:CC988;SN:MY7CIH510P0506;S:038088C4840010210078cb0000041b8042746b8044847b8044e44b8046448b8005545b80464;Z:0102,05000009016a85013245013245013245013241013245!sT\xf0\xa0)M}!sU\xac\xff\xff\xfa@\xa09\xc7?)(x-hp-guid=001e0b9a5ccc)'