I had so many issues with this, it feels like you have to keep track of whret you do changes and when it has synced it. Otherwise it won't merge and you will have to do it manually.
Honestly, I think I had syncing conflicts maybe once or twice, and even then the merge feature worked without any hiccup.
Maybe it does help the fact that I have my NAS always online, and I treat my mobile devices mostly as "read-only" - i.e, if I have to create a new password it will almost surely be on my desktop / laptop.
Bitwarden is so much easier sadly.