Here is a quartz crystal inside the 32.768KHz tuning forks crystal, it is easy to cause breakage of the crystal when it impacted or dropped, and the crystal is ineffective.
The oscillation stability reduces due to the increase of Crystal Impedance (CI).
When the CI value is significant, the starting or stopping voltage becomes high. That is, even if the voltage increase, it is difficult to start the oscillation. Also, the voltage slightly lower, and the oscillation becomes unstable or stopped.