This appears very similar to Syncthing not syncing Obsidian vault: "Up to Date" but changes not propagating (GrapheneOS Pixel 8 + Debian 13) - #2 by gadget. I will include some logs.
Issue: Syncthing v2 client on Pixel 8 isn’t syncing with v1 server on Debian. However, a Syncthing v2 client on a Pixel 6 continues to connect to the v1 debain syncthing server just fine.
The client shows these logs:
12:52:05W/libsyncthingnat type=1400 audit(0.0:19841): avc: denied { bind } for scontext=u:r:untrusted_app:s0:c16,c256,c512,c768 tcontext=u:r:untrusted_app:s0:c16,c256,c512,c768 tclass=netlink_route_socket permissive=0 bug=b/155595000 app=com.github.catfriend1.syncthingfork
12:59:32I/com.github.catfriend1.syncthingfork Explicit concurrent mark compact GC freed 8492KB AllocSpace bytes, 511(10MB) LOS objects, 75% free, 8819KB/34MB, paused 129us,649us total 23.469ms 12:59:32I/com.github.catfriend1.syncthingfork Explicit concurrent mark compact GC freed 792KB AllocSpace bytes, 72(1440KB) LOS objects, 78% free, 6715KB/30MB, paused 118us,381us total 16.072ms 13:02:16W/libsyncthingnat type=1400 audit(0.0:20076): avc: denied { read } for name=“route” dev=“proc” ino=4026532018 scontext=u:r:untrusted_app:s0:c16,c256,c512,c768 tcontext=u:object_r:proc_net:s0 tclass=file permissive=0 app=com.github.catfriend1.syncthingfork 13:02:20I/com.github.catfriend1.syncthingfork Explicit concurrent mark compact GC freed 4913KB AllocSpace bytes, 36(880KB) LOS objects, 75% free, 9204KB/35MB, paused 168us,720us total 24.981ms 13:02:20I/com.github.catfriend1.syncthingfork Explicit concurrent mark compact GC freed 1924KB AllocSpace bytes, 39(1200KB) LOS objects, 79% free, 6175KB/30MB, paused 143us,476us total 19.167ms 13:02:21W/ConfigXml getFolderIgnoreList: File missing /storage/emulated/0/Documents/3050-Vault/.stignore 13:02:21I/Util Successfully wrote test file ‘/storage/emulated/0/Documents/3050-Vault/.stwritetest’ 13:02:24I/AutofillManager onInvisibleForAutofill(): expiringResponse 13:02:25W/libsyncthingnat type=1400 audit(0.0:20099): avc: denied { bind } for scontext=u:r:untrusted_app:s0:c16,c256,c512,c768 tcontext=u:r:untrusted_app:s0:c16,c256,c512,c768 tclass=netlink_route_socket permissive=0 bug=b/155595000 app=com.github.catfriend1.syncthingfork
The server GUI under Remote Devices for this device shows I/O timeout, and there are no logs in the log file for this device.