This is a topic for reports of index anomalies. Syncthing debug messages refer to this thread in which reports can be made. If you ended up here as a result of seeing an index anomaly in the Syncthing logs or GUI please paste the message you saw and any relevant things you were doing at the time. Thanks!
Ideally, this will be removed in a further-future version and this topic can be closed with an explanation.
ELI5 tl;dr: we’re adding a canary to check for unexpected badness
For the purpose of hunting down an index corruption/“things look out of sync” bug that has been around for quite a while, that we never managed to reproduce.
2024-09-12 14:33:12: Index sequence anomaly detected (please report at Index anomaly reporting): index update with unexpected sequence (map[batch:1000 expectedPrev:361110 lastSeq:363960 prevSeq:362545])
Popped up while I was rebuilding a wiped folder by resynching…
Very interesting, thank you for reporting! Can you describe a little more the steps involved in this rebuilding?
2024-09-20 23:26:45: Index sequence anomaly detected (please report at https://forum.syncthing.net/t/22660): index update with unexpected sequence (map[batch:18 expectedPrev:1791693 lastSeq:1791693 prevSeq:1791675])
Restarted SyncThing via the Synology Package Center. Currently running on v1.27.13-rc.1, Linux (64-bit Intel/AMD).
The local copy of a folder shared by 4 peers got mostly erased (through ‘n’ lexically…) and Syncthing was not running. I restarted Syncthing after touching .stfolder and started synching with the other nodes.
It ultimately finished synching (~70GB, thousands of files) and the error did not reappear.