Larian Studios Forums Divinity: Original Sin 2 Divinity - Original Sin 2 - Bugs & Technical Problems Multiple GM Mode and Divinity Engine 2 problems.

I did a bit more testing. Unsubscribing and delting all Definitive Edition mods fixes the issue but sunbscribing to even just 1 mod for GM Mode in DE (even if it's just a map) the error will reappear.
It looks like the latest patch did break modding for GM Mode.