Bridges shifting or jumping during playing is a fairly common occurrence. It is rarely down to a single cause, so it needs to be worked through item by item.
One common cause is insufficient string tension. When tension runs low, the string does not press the bridge down firmly enough, and the vibration of playing can push the bridge out of place.
A shortened vibrating length can produce a similar problem. If a bridge sits too close to the front nut, the load on that string segment changes and the bridge becomes less stable.
The height of the bridge and the condition of its foot matter just as much. Poor contact with the soundboard, or too little friction at the foot, both reduce stability.
A sensible order is: confirm the number and position first, then check tension, then check the condition of the bridge itself. If the problem keeps coming back after you adjust it, ask an experienced teacher to look at it.