Blanc

The game is still new and has annoying problems to run in online coop properly.
On switch version the game can crash for player 2 after some cutscenes skip.
On PC version the player 2 can be disconnected.

If you play on PC, you can use a software called "Parsec" to avoid this problem.
Parsec will remote your desktop for your mate and simulate local co-op play with low latency that avoids online game glitches like disconnects, crashes, or the invisible wall if you skip the Chapter 5 ending cutscene too quickly.

This is only a temporary solution, hoping the devs will create a patch to fix this issue, but for now it only works with Parsec or similar software.

For switch players I don't have the solution yet sorry.

You can find the link for download the tool in "ressources".