Apologies for the delay in replying. I have a couple of more questions and some things to possibly check for potential problems.
1. Is the Oil removal unit strictly for removing oil, or also a dryer? (I would recommend a dryer be installed if one isn't there)
2. Have you considered a receiver upstream of the oil removal unit (dryer)?
3. Does your receiver have a timed drain to remove any condensate buildup?
I would check the receiver for possible condensate buildup. Verify that your timed drain, if installed, is working correctly. If working and still getting condensate buildup, you may need to change the timer to drain more frequently, especially in summertime.
Check your smaller compressors and make sure the variable flow capacity valves are modulating properly to unload the compressors when appropriate.
Use a clamp meter to verify the current on the smaller compressor motors is actually exceeding the trip setpoints. Check the integrity of the electrical connections to the smaller compressors from the Motor Control Center to the motor terminal boxes. Preferably use an infrared camera and inspect for hot connections. If you do not have an infrared camera and cannot obtain one, shut down and lock out the compressors one at a time and inspect the connections manually and clean and tighten to proper torque as required. Make sure you insulate them properly when completed.
I hope this helps. If you have any additional questions, please reach out.