Since the units are in the same bus, swells might be occurring internally or harmonics is a possibility. Root cause might be
1) old hydraulic fluid (a slight change(increase) of viscosity can result to increase in pumping load) like a hypertension
2) clogged plunger,valve or hydraulic line, uncalibrated pressure sensors/switches and guages
3) pump issues, like failing bearing or misalignment, or worn impellers
4) Failing Drives (IGBT's tend to short circuit when failing. 3 line has each own set of IGBT's if one is failing its additional load to both remaining)

I would rather recommend owners to isolate each motor/lift with an AVR plus a surge protector. By that, I can be sure that power supply quality is not the issue since harmonics and swells can be directly eliminated with its aid. AVR won't cost much than a burnt motor or control board or drive to replace.

I have no problem with my previous installations I have with AVR, the only sad thing is you don't have much electronic parts to sell cause it does prolong pcb and sensor life. For eight years I have not even changed an LED lights of the cabin. Only mechanical parts.