The conflict files appear when you open a file, do some modifications and you save a file, and if in between the opening and the saving, someone else touched the file as well. Then there might be conflicting changes to that file and the automatic sync process cannot decide which version to prefer.
It can be that some software doesn’t do actual changes, and just changes the modification date, that might be already enough to consider that as a ‘change’.
If you want to track down these cases, it can help to go through the webserver access log and see which clients accessed/modified a file while you were editing it. And if it is really related to actual changes. In such a case you have options to handle this better:
I you want to work on a document together, it is more suitable to use online-office solutions where you can open a document with different online clients at the same time.
If you want to manage different versions of text and have several people working on it, git might be interesting as well. You can have branches, check merging different changes etc.
In Nextcloud you have collabora (https://nextcloud.com/office/) or onlyoffice (https://nextcloud.com/onlyoffice/). I don’t remember the exact limitations, there were some like the max. number of parallel users was 10 or 20, so it is free but for commercial use (= if you need more), you have to pay or compile yourself.