Recently, I had a couple of crashes in the battle with demons near the teleporter on Blood Moon Island. It seems to be related to "blood spit" and happens near the end of the battle. Concentrating on killing the two creatures first with "blood spit" capability (they look like floating viruses) seems to prevent this from happening.
I have a similar problem, my game crashes after the enemy uses "Madness Squall". Turning Graphics down didnt change anything. Also, this is the first time my game Crashed at all, so i dont think its anything related to my PC Setup.
Please email firstname.lastname@example.org with your save in combat where this can be reproduced (or a Dropbox or Google drive link, etc). If you are using any non-Larian mods, also include a list of those enabled and/or the modsettings.lsx file from your profile folder. Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin 2 Definitive Edition\PlayerProfiles\<ProfileName>\Savegames\Story' folder. In Windows Explorer you can zip a file or folder by right clicking on it/them and selecting 'Send To | Compressed (zipped) Folder'.
Unfortunatly i already killed the Mobs and left Reapers coast, my solution was to keep them in a CC chain, so they cannot cast "Madness Squall". If i happen to run over this Crash again, i will proceed as you suggested.