Bitzer 4t.12.2 oil foaming

[blissy123]

I have bitzer compressor which is going out on low pressure differential switch occasionally. The only thing i can find is that the oil sight glass foams as soon as the compressor starts and keeps foaming. It has a 18K superheat at the compressor just running one evap with TX. I have the same problem on another exact compressor at site but the other five are all running fine with no foaming of sight glass.

Any help would be great

Thanks