Regular power failures - RCD tripped
Very interesting. My guess would be that when some large piece of machinery switches off (or on), it causes a huge shift in ground current that extends through your property, and this impulse is what's tripping your RCDs. You probably wouldn't see this on a multimeter; you'd need a datalogger with a reasonably high sample rate to catch it.

I'm thinking that to solve the problem within your firm, you'll need to carefully isolate all of the ground connections for every piece of equipment downstream of the RCDs and tie them back to a single point, like they do in hospitals for sensitive equipment (usually indicated by an orange-colored outlet or other marking). However, depending on how extensive your facilities are, this could get to be as expensive as an UPS (but would be lower maintenance, long-term).

The other approach would be to get the power company involved and see whether they can make any adjustments at the substation or have any other advice for you.