Update 2
Ich habe ein altes Snapshot (8.Februar) gebootet und siehe da, der Scanner funktioniert wieder (Quellcode für simple-scan --debug unten).
Offensichtlich verwendet dieser alte Snapshot die Version 3.34.2 von simple-scan, während im Ausgangsthread simple-scan 3.34.4 verwendet wird.
Zusatzinfo: ich nutze Gnome 3.34.3 -- vielleicht gibt es diesbezüglich Probleme?
Vielleicht hilft diese Information weiter?
felix@tux:~> simple-scan --debug
[+0,00s] DEBUG: simple-scan.vala:638: Starting simple-scan 3.34.2, PID=4129
[+0,01s] DEBUG: _g_io_module_get_default: Found default implementation dconf (DConfSettingsBackend) for ‘gsettings-backend’
[+0,05s] DEBUG: app-window.vala:1691: Loading state from /home/felix/.cache/simple-scan/state
[+0,05s] DEBUG: app-window.vala:1670: Restoring window to 757x400 pixels
[+0,05s] DEBUG: autosave-manager.vala:64: Loading autosave information
[+0,05s] DEBUG: autosave-manager.vala:259: Waiting to autosave...
[sanei_debug] Setting debug level of dll to 255.
[dll] sane_init: SANE dll backend version 1.0.13 from sane-backends 1.0.27
[dll] sane_init/read_dlld: attempting to open directory `./dll.d'
[dll] sane_init/read_dlld: attempting to open directory `/etc/sane.d/dll.d'
[dll] sane_init/read_dlld: opendir failed: Datei oder Verzeichnis nicht gefunden
[dll] sane_init/read_config: reading dll.conf
[dll] add_backend: adding backend `brother4'
[+0,09s] DEBUG: scanner.vala:1485: sane_init () -> SANE_STATUS_GOOD
[+0,09s] DEBUG: scanner.vala:1491: SANE version 1.0.27
[+0,09s] DEBUG: scanner.vala:1552: Requesting redetection of scan devices
[+0,09s] DEBUG: scanner.vala:806: Processing request
[dll] sane_get_devices
[dll] load: searching backend `brother4' in `/usr/lib64/sane'
[dll] load: trying to load `/usr/lib64/sane/libsane-brother4.so.1'
[dll] load: dlopen()ing `/usr/lib64/sane/libsane-brother4.so.1'
[dll] init: initializing backend `brother4'
[dll] init: backend `brother4' is version 1.0.1
[dll] sane_get_devices: found 1 devices
[+0,10s] DEBUG: scanner.vala:341: sane_get_devices () -> SANE_STATUS_GOOD
[+0,10s] DEBUG: scanner.vala:353: Device: name="brother4:net1;dev0" vendor="Brother" model="DCP-9022CDW" type="DCP-9022CDW"
[+0,15s] DEBUG: autosave-manager.vala:281: Autosaving book information
[+0,25s] DEBUG: app-window.vala:1752: Saving state to /home/felix/.cache/simple-scan/state
[+1,78s] DEBUG: app-window.vala:1752: Saving state to /home/felix/.cache/simple-scan/state
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