Files/documents became unavailable

The problem was in ownCloud. I set up from scratch nextcloud, the problem is here too.

Sometimes my files/documents in Nextcloud disappear. They are in the index I see thenm in the web-interface but I can’t download them. From the interface ut seems like they are but I have an error when try to access them.
When I look at file structure I see a new directory (for example today it’s: GNUSparseFile.4788) and all files there with only 11 first characters of their names left.

Nextcloud lives in a lxc-container on zfs. All files are in UTF-8 (Russian) ownCloud with the same problem was on apache with mysql, nextcloud is on nginx with PostgreSQL.
I use web-interface and nextcloud desktop client.
I have a lot of directories in nextcloud and this happens only on some of them. Some time everything is ok and sudenly files disappear.

Where shoul I look?

Do you use external storage or encryption app? Are the disappearing files with cyrillic filenames or does it happen with ascii-only names as well? Did you find any hints in your logfiles?

No external storage, no encryption app.All the desappearing files are with cyrillic filenames. But the most of my files are with cyrillic filenames.I don’t see any hints in my logfiles but maybe I just don’t know what and where to look for,

You can try and check the bugtracker for similar issues. Did you try to rescan your filesystem, does it bring back these files: occ files:scan username
Are there a lot of files/folders?

I didn’t find any similar issues. Maybe I searched in the wrong place.
It’s zfs, so there is no fsck or other file system scan. The files are on the disk but in strange GNUSparseFile.4788 folder with shortened names.
It’s a server with a lot of lxc-containers. All are on the same zfs. No problems with the other containers. No server crashes etc.
The problem is only with lxc-container with nextcloud. Maybe it’s because of a lot of files with cyrillic names. It may be a file system issue but it happens only with nextcloud. I reinstalled it from scratch, the same problem. It doesn’t happen always, only sometimes, I can’t find any system in it.

And the occ command I wrote? That is a Nextcloud command to reindex all the user folders to update the file-index table. Cyrillic could be, if it happens with a few files as well, you can try on Another idea would be to test on a virtual machine with the official vm-images: