While we can't share specifics, if you believe the Copyright strikes are invalid, here are a few ways to resolve them– get a retraction or submit a counter notification. Here's more info: https://yt.be/help/fhTF . Hope this helps.
I understand deleting a video does not remove a strike. Does that mean a strike can not be undone if the video has been deleted,, even though both parties are willing to retract the strike?