I’m trying to figure out if you are monitoring the signal coming into your interface before it gets to Cubase or if you are monitoring the signal after it is received by Cubase.
I’m not familiar with the UR28M, but it appears to have some sort of “Latency-free DSP-powered monitoring”. Are you using this feature? You might want to check out the Direct Monitoring checkbox in Cubase’s device setup.
It sounds like an issue relating to your interface setup within Cubase. Maybe another UR28M user will be able to provide you with some more assistance.
Have you tried posting in the Steinberg Hardware forum? Or maybe search through the topics there to see if you can find something similar to your situation.