Touch is legal; knock-off is a miss
A bar that shakes, tips, or even lifts slightly off the pegs and settles back down is a make, full stop. What ends the attempt is the bar actually leaving the standards before you've cleared and landed. That distinction matters because vaulters at any real height are going to make contact somewhere on the way over; the technique goal isn't avoiding the bar, it's clearing with enough margin that contact doesn't carry enough force to knock it off.

