Double Popping on FHS Vault

[CoachKel]

I have a gymnast who is double popping on vault. She had a great HS flat back last year. We have a prota-vault that goes into our pit and she doesn't do it on there. Once she gets to the table it's like she double pops and she almost get stuck in her HS. Any tips or advice on this situation I've tried many drills and nothing has worked!