SQLite error 3850 when exporting backup

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User reports that Delta Chat desktop 1.46.5 installed from flathub fails to export backups into home directory. The error is displayed in a toast: "IMEX failed to complete: could not export database: failed to attach backup database: disk I/O error: Error code 3850: I/O error in the advisory file locking layer". The whole home directory has eCryptfs mounted from ~/.Private into ~. Underlying filesystem is ext4.

I have tried the same version of Delta Chat desktop from flathub and it successfully exports backups. I don't use ecryptfs though.

I have tried to reproduce the error by installing ecryptfs-utils, running modprobe ecryptfs, creating a new ~/.Private with ecryptfs-setup-private --nopwcheck --noautomount and mounting with ecryptfs-mount-private. Delta Chat desktop then successfully exports backup into ~/Private even if I run desktop with XDG_CONFIG_HOME=$HOME/Private/config to place account folder into ecryptfs as well.

I have not tried to run Delta Chat desktop inside flatpak and exporting into ecryptfs. Maybe there is some bad interaction between flatpak and ecryptfs. If this does not fails as well then I don't know how to reproduce the problem.