Problem with my vfc mp5

Ive had a VFC mp5 v1 for a while now and recently i took it out again to use and while the selector is in semi, I gets through a few shots no problem than shoots full auto uncontrollably, ive brought it to a shop and they dont know whats going on. I was hoping someone here could maybe guide me or give me a few things to check? Ive replaced the fire selector already as they do have a problem with wearing

I can attach a video of whats its doing if needed or photos of certain parts