Machine consistently pausing briefly, after 15-20min in to a job?

[magicniner]

When you say it stops then carries on you don't say if code continued to run and moves were lost or if the code stopped running?
Assuming the code didn't stop running then your problem could be a PSU which isn't coping any more and is cutting out briefly with thermal overload, but don't assume and don't guess, test it under load with a meter.

P.S. never ignore un-programmed behaviour in a CNC system, if it's doing something other than exactly what it's instructed to do then something is broken and needs fixing!