There is a general consensus on the forum that USB interfaces are more susceptible to electrical noise than ethernet, and general advice is to chose ethernet over USB for this reason. However, no-one here can state whether this would fix your issue (I suspect it'd certainly help).

First things though - can you not try to dampen your electrical noise - get some ferrite filters for your compressor (remove noise at source) and IEC leads for your CNC get-up. <- that might not be very effective - yeah, some noise when switching an induction motor on/off, but not as much as a brushed motor.

A UC300ETH would, as well, open you up to try the UCCNC software, rather than Mach3 - I for one much prefer this, I know this is a view shared with others.