Two player career mode won't open

So me and my friend just had the same problem recently and i may have found a fix since it worked for us.

Whoever is host of the two player career mode needs to load into the career mode from the main menu and select the option "Replace Player". Once you have done that it will warn you about removing the existing player, just select "Continue"

After that restart your entire game and load it back up, then once again load into your two player career mode. You will notice that your friend has dissapeared, this is good. After that you simple press "Invite Friend" and select the friend you was playing with. They should then get an invite within their ingame inbox.

Once your friend accepts he will then simply join back into the session, his/her stats and progress will have saved and be back to normal, however be patient. It will take a few minutes maybe more to join back, it took my friend around 3 minutes to finally load in but that might vary based on internet speeds.

This worked for me but i am on PS5, but give this solution a go and hope it helps.