This is the first time I've seen this and I've went through all the troubleshooting steps but it still keeps happening.

My sim who is teen asked his best friend who is a YA and a Celebrity to be his girlfriend and right after he did that he jumped a little back and when I tried to have him socialize with her the only interactions available where those you that you get when meeting a celebrity for the first time all other interactions were lost. Resetting my sim or removing her Celeb status puts everything back too normal but I've never had to that before.

I dunno if that was it then removing resetting him wouldn't change anything plus even after 9 days their still boyfriend and girlfriend I usually would have to use MC a couple of time to make it stick. The only thing I've seen the game do is change the relationship to romantic interests but not completely take away interactions even Woohoor's Interactions where lost.

Funny you should mention that as I was able to.

But here is where it gets a little strange the only thing different is that I installed ITF but when I uninstalled the issue disappears

This issue seems to be more related to a conflict of teen LTR categories vs values than it is to the celebrity system. With adults, "Romantic Interest" has a higher place in the hierarchy than even "Best Friend". With teens RI ranks even lower than "Friend". I first noticed this issue with my teen losing the ability to "Learn to Drive" when even a housemate became a Romantic Interest.

With teens, it doesn't matter how high your LTR numeric value is. A "Romantic Interest" will not count towards the number of friends a Sim has, unless they become boy/girlfriends.

Using Selector to briefly make the YA celebrity the active Sim and initiating contact with them, I was able to get my teen to interact normally (romantically) when I switched back.