Yesterday I posted a video of me playing Toxikk, and immediately there were 4 copyright claims.

Does Reakktor Studios know about possible claims ? If so, it might be worth mentioning the possibility of a claim on game's homepage.

Were you using music? I have seen multiple people Stream and Post Multiple Youtube videos just fine, a lot of people do turn in game Music off as this may cause it to flag. Double check what your posting does not have any additional Copy write content.

Its just recording a game (including music)..

Tried it with a new account (with no monitisation), and it still's going on

They said that TOXIKK was free to monetise so I have no idea tbh

I'm generally using DailyMotion now, so for YouTube all the music will need to be replaced I think...

Reakktor is the copyright holder of the visuals, and they allow you to use it in your youtube clips.

The audio material is licensed from 3rd parties, meaning that someone else holds the copyrights.
If you want to use that audio, you also need to get a license from the copyright holder.
And since that isn't Reakktor, they have no control over the copyright claims, which is something between the copyright holders, YouTube and you.

That's what comes of not having an internal music department

Yes that my be true, however that is also most costly, and a temporary position at best, however Why would anyone have "In Game Music" being played anyway? That seem's rather odd for an FPS to listen to Music instead of game sounds. Pretty sure I mentioned this originally. "MUSIC" is the #1 way to get a Copyright claim from Youtube or even Twitch