I had something similar happen in Logseq when I stored my main directory in Sync, which is similar to Dropbox. After moving my main directory out of Sync, everything became stable again. Perhaps Dropbox was the root cause of the problem.
The problem could be the way you used the directory. I don't know Sync specifically, but DEVONtech don't recommend storing the databases in directories which will be synced. Rather you are supposed to set up the system to use whatever sync API is available, which presumably makes sure files are internally self-consistent before syncing. It's a while since I set it up, but that's how I did it with WebDAV to my NextCloud server.
