alt Hacker NewsI actually had a similar thing happen with gvfs-fuse (Google drive). It was a bug in gvfs using the quota usage of a file as it's file size (because libgdata didn't provide a method to get file size), but I was using a file shared to me so it had zero quota usage.
All of which is to say I would bet on something in the webdav-nextcloud line being at fault instead of keepassxc.
I sync'd this file using various means on different platforms, nextcloud apps on windows using virtual files and android with Storage Access Framework cloud integration, and on linux with rclone and somehow never had such a catastrophic issue