Two carlyle 06d compressors twinned together with a common oil line between them. The application is a walk-in freezer maintaining below 0F using R507 & POE oil. Thermostat/defrost control is a Johnson digital with remote sensors, controlling lls for pumpdown. Defrost is 30min every 6 hours timed termination (electric). I receive a call that it's not keeping temp. I ask the customer if the oil failures had tripped, yes they did when he reset them, three times they failed. That was yesterday at 2:00pm twice and the third at 11:30pm. Today I get there around 8:30am and reset both controls. Take oil pressure, 19-21psi net. Oil S/G is half full. I tried to simulate a situation where one compressor would run and not the other, it didn't trip. I couldn't force these compressors to trip. My only conclusion is that there wasn't oil in the crankcase yesterday, and for some reason there is today. Is it possible for the oil to slowly return overnight? If so, am I looking at a piping problem? Why overnight and not between 2:00pm and 11:30pm? Thay have a blast freezer in this box as well, so thay let that run to maintain temp.