It Takes Two - "The other player has left the session"

I'm playing It Takes Two on my Steam deck, and we've made it almost to the end of the game. But we keep crashing every so often, sometimes after an hour, sometimes after 10 minutes its random and always gives the message the other player has left the session. This issue only began in Rose's room, not before, and hasn't subsided.

What gives? is it from lag we do have very high latency sometimes, and is usually before a crash. 

Hi @ThePookaDragon Would it be possible to try the following steps?

• Clear the systems cache (Close the game completely > Turn off the console > Wait 30-60 seconds > Restart and Relaunch)
• Verify you signed into your PSN account
• Check for updates 
• Restore Licence
• Try the steps in our Connection and Advance Connection Guides 
• Open your PS5 NAT Type
• Change DNS settings (You can use the public google DNS primary: 8.8.8.8, secondary: 8.8.4.4, unless there is a different DNS you would rather use)  
• Entering Safe Mode and Rebuild your PS database

So I was able to convinced my friend to play It Takes Two and we were having a blast. But as soon as we finish the bull boss fight in the Cuckoo Towers, my friend will crash and the game will say ‘player has left the server.’ 

And it will take us back to the boss and when we beat it again, my friend crashes once more. 

we both own PlayStation 4 and we don’t know what to do. Does anyone have any suggestions?