Is there an error message?

Clicking on one of the rifts should generate a new full battlefield (one of the versions from the first 4 acts).
Did you have any issues with the battlefields during the main game?

Try clearing the dynamic folders for all of the acts.

Try lowering the game resolution.

If you check the Event Viewer, does that give an error code or 'Faulting Module' file name that might help identify the cause of the crash?
- click Start (or WinKey-R), then type "event viewer" into the search box. in Windows 10, 'event' should bring up 'View event logs'.
- after starting the Event Viewer, expand 'Windows Logs' in the left column and select 'Application'
- in the center column, look for a recent error for the game (maybe sort by Date and Time, or search for 'div.exe')
- check the information under the 'General' tab below the list of events, starting with "Faulting application name..."


If you zip your act 5 save and email it to support@larian.com, I can see if I have the same problem here.
Each save is a folder in the '..\Beyond Divinity\savegames' folder.
In Windows Explorer you can zip a file or folder by right clicking on it/them and selecting 'Send To | Compressed (zipped) Folder'.


BTW, if you didn't already do so, just before stepping through the final rift, you can have the Deathknight unlearn all skills (if you have enough gold) and invest everything in the summoning doll upgrade skills (IIRC I boosted level a bit, and then split the rest between range and the skill point transfer).
Since the purpose of the main characters is to undo the soul forge, it shouldn't be spoiling anything to say the after-game battlefields are just the hero, and summoning dolls.