Ryobi 524 GX, impression not turning on

My operator came to me with an issue I have not seen before. Running a 07 524 GXP, were running CMYK, all units are turned on. However randomly when starting up unit 2 will not engage but units 1,3 & 4 will. Then another time during the day Unit 3 was not engaging while 1,2 & 4 will. This just started today, happened only on startup. Turn press off then on, problem goes away temporarily. No low water pan error or any error message at all. Thinking there would be oil in a connector, not sure where to look now. Anyone experienced this before?

 

Could it be low air pressure? Or if not low overall, perhaps a leaky line in there somewhere.

 

Good point. Have not had the issue come up since Tuesday, The compressor is appears to hold good psi level. But the compressor we have is much older than the press. Something to look into. Thanks for the suggestion we were overlooking...