So I looked this up. Apparently this has been an ongoing issue for 2 YEARS with no fix.
The cutscene in the oracle mission where the heratic is behind the ray shield will boot both players back to the main menu. And the cutscene where Johnson teams up with the arbiter on the great journey also boots both players back to the main menu unless they spam skip.
This is honestly game breaking and really disappointing. Why have these never been fixed?