upfront - I’m not a KPDX user. But I look at webdav issues and storage access framework.
The position of the app author: I use the SAF - it’s up to the backing storage provider (nextcloud app, then the network remote) to get its things in order, as in: caching, handle concurrent writes, invalidation & refresh, network latency in general.
Imo if you want a networked password manager use one that has a backing API (the likes of bit-/vaultwarden) that does atomic actions (per item) or something like pass + gpg + git remote if file based.
If you insist on one database file, save locally and have a second application do an explicit sync (not SAF implicit). With SAF webdav mounts I’ve seen catastrophic 0 byte writes to the remote, kpdx too. It’s not the apps fault, but still, ouch