Halo MCC - "Connection Interrupted" , and other problems.

Hi. So I'm not sure if this is your side or what. First off, it was a headache to even connect to a friend, we couldn't see each other off and on (both in game and with the PC Xbox app; going on/offline when we actually weren't).

So I did some research and started with both of us restarting our routers and rebooting our PC's. She then could join me (I still couldn't see her), and I was able to start the Halo CE campaign's first mission. It started to load, then: "Connection Interrupted.
Your connection to the game session was interrupted".

The next time I joined her (she has higher internet speeds but lower loading times typically), and we got past that message. Could be coincidence, but we tried the previous step a few times with the same results. The first mission loaded and started. Then,
about 10 minutes in, the connection was lost upon entering a corridor (indicated by an error message in game).

We have the proper PC and internet specs to run this game, so this should honestly be pretty seamless.

Now, I'm going down a rabbit hole of troubleshooting, involving hosts having a regular hard drive vs a solid state drive (times out if the loading is too slow on either side), forwarding ports (did that, but if this is the case I could be missing some -
wouldn't think I'd have to do this), and even joined an Xbox club through the app (seems odd, but worked for some).

This is all completely ridiculous with a AAA game (a remaster!) and company as huge as Microsoft. I just would like connect to the game with a friend properly.

I am sorry to be blunt, but I would really appreciate a fix. Instead I'm browsing numerous forums with people having the same issue with no fix, or one that has not worked for me.

Thanks.

:)