Unexpected real time delay on servo system

Thanks all for your replies.

My field 24V is supplied from one of the original Bridgeport power supplies, I'll be surprised if it's not man enough. Could definitely be wiring though, I'll check what I used tomorrow.

That error indicates rather severe EMI

Do you have a snubber or arc suppressor on the relay contacts?

Without an arc suppressor, arcs at relay contacts act as quite effective
pulse radio transmitters with frequencies from KHZ up t GHz

nope.. I'd never heard of a snubber before. That's something I can look into! Thank you.