I am aware of servo amp power supplies and servo amps failing. The UPS for the server room also sends high and low input line voltage messages.
The one servo power supply I opened up has a a rectifier module that has a 3 phase input and 2 wire DC output. I assume it is a 6 diode rectifier and that will generate the 5th and 11th harmonics.
I believe there are several things going on concurrently. Excessive harmonics, utility surges and sags, transients both internally and externally generated. No idea yet if there are also redundant N-G connections, poor connections, or a deteriorated ground networks. The building is 100+ years old with multiple additions.
To add to the fun, there multiple types and manufacturers of each type of machine.