For me the issue was that I was using the incorrect Data path for creating Definitive version mods as explained here:
http://forums.larian.com/ubbthreads.php?ubb=showflat&Number=639075#Post639075I was using the path from the Divinity Engine 2 Wiki:
..\Steam\steamapps\common\Divinity Original Sin 2\Data
but the problematic errors all disappeared when I used this path:
..\Steam\steamapps\common\Divinity Original Sin 2\DefEd\Data
The "resource file is newer (version: 3.6.2.0) than your code version (version: 3.6.1.0)." errors I have read on Discord are nothing to worry about.
After changing the data path as shown above* I have been working my way through the following Add-On tutorial without any significant problems:
https://www.youtube.com/watch?v=zHf_wNTDNIo* I also reinstalled Divinity Original Sin 2 and the Divinity Engine 2 but from what I have read elsewhere this was not necessary.