Looseness is probable. Looseness could be between parts that are inspectable externally or it could be an internal problem that can only be verified by opening the parts. Example is bearing inner race OD and shaft.
In my word, amplitudes like 24 mm/sec are too high to keep the machine running or keep the operators check the machine. Safety is important.
Have you inspected the lubricant (drained the oil to check it)? Any observations like unstable reading, noise, high temperature were noticed?
Regards- Ali M. Al-Shurafa