Hi! Just to get a few questions out of the way...
Are you playing with mods? Does it happen without any installed/enabled?
Have you tried all the common solutions, such as verifying game files or doing a reinstall, create a new player profile and try with that, etc?
If so, here's a compilation of suggestions that I've noted to be given by support in similar cases... Also, make sure to try disabling any overlay programs you may have, such as Overwolf, Discord overlay, etc. Check for any apps that is intended to alter game performance too, I know Razer has one, then there's 'gedosato' which turned out to cause problems with DE for one user on Discord. Disable those too.
- Try exiting out of the Steam client, and starting the game directly from the '..\SteamApps\common\Divinity Original Sin 2\DefEd\bin\EoCApp.exe' program file, by right clicking and running as administrator (or '..\Divinity Original Sin 2\Classic\EoCApp.exe' for the original release).
- If applicable, disable Steam cloud support either globally (in the client click on the Steam menu and select Settings, and then Cloud) or just for this game (in the library right click Divinity: Original Sin 2 and select Properties, then switch to the Updates tab and check the Steam Cloud section).
Alternately, exit out of the Steam client, or Galaxy for the GOG version, and just start the game directly from the executable when required. - Try doing a clean boot and then test the game. Click Start, or hit WinKey-R, type in msconfig and hit enter; in the General tab, click Selective Startup, uncheck Load startup items (if required) and leave Load system services and Use original boot configuration options checked. Next, click on the Services tab, check the box to Hide all Microsoft services, then click the Disable All button (maybe make a note of which are currently enabled/disabled), then click OK and reboot the computer.
Run msconfig again to switch back to the normal boot configuration.
If that doesn't help, you could email supportdos2@larian.com with a dxdiag report (WinKey-R, type in dxdiag and hit enter, then when it finishes loading click on the 'Save All Information...' button and save the report somewhere handy). Also check the '...\Divinity Original Sin 2\DefEd\bin' folder for the gold.log file, and if any 'CrashDump' files are being created, zip the most recent dumps together to include and attach that in the mail.