Some centrifugal pump designs utilize this type of bearing as a radial bearing. Too much shaft vibration and no vibration damping. This is a big problem with the metal bellows seals we find in high temperature applications. Vibration damping interferes with the frequency of the vibration. The O-ring found in many seal designs is a natural vibration damper.
Harmonic vibration is a major source.
The seal is vibrating in harmony with another piece of equipment Cavitation is very common in many applications. Remember that there are five types of cavitation and all of them can cause vibration problems. Slip stick vibration can occur between seal faces if the pumping fluid is not a lubricant. Hot water is a good example of a non-lubricating liquid. Most gases and dry solids are obvious non-lubricants.