On the front side of the movement is the rack which falls down to the snail (on the minute arbor). It is gathered back up, one tooth at a time while the strike sequence is going on. When it reaches the last tooth, the rack hook should drop over the end and the strike should stop. One or more of those things are the issue. You'll have to observe to see which it is.
Often it's a little shiney stamped lever that does the actual stopping of the gathering pallet. Over time it gets bent slightly and pops up instead of stopping. Just study this area, while applying an extra 4 or 5 pound downward pull on the left weight. The extra force can cause the stop mechanism to 'show it's hand'. Willie X