Database inconsistency when using rest/db/browse request

[galilley]

What happened?

Hi All!
Recent time I observed problems in using the REST API to go through the file tree, especially, in the GET /rest/db/browse request, on which the project pyselsctive is based on.

Observation

My use case is a one NAS storage with a big folder and about dozens clients who use ignore patterns to sync a few sub-folders of interest. I've been using it for a year but recently my app started to crash with new clients. Brief debugging shows one request fails randomly (different folders for different user):

$ curl -X GET -H "X-API-Key: xxx" -k "https://localhost:8384/rest/db/browse?folder=shared-folder"
could not find child 'people' for path 'people/family' in parent ''

The same occurs with parameter levels >= 1, but works for levels=0 in combination with prefix=people and prefix=people/family or without prefix. However, the folder 'people' is not enumerated. So, I can not replace request with levels=1 by two nested loops with levels=0.

It should be noted that a problem folder can be different for another client.

Reproduction steps

I'm really do not know how to reproduce such behavior based on a constant year long using of SyncThing... I only can attach some additional info and do some experiments to localize the problem.

info-people-family.txt
info-people.txt
infonas-people-family.txt
infonas-people.txt

Syncthing version

1.23-1.27

Platform & operating system

Win32, Linux

Browser version

No response

Relevant log output

No response