Hi there,
I had this issue today after updating to Cubase pro 9.5. I noticed you have an mr816 in your bio. I also have this unit . the problem for me is the fire wire driver loosing sync with the hardware. Even though you still hear audio coming through the device if you check its own settings and where it shows you what version of boot and driver etc you may notice it is blank. close Cubase and physically switch off the mr816csx and back on then open Cubase you should find it solves the problem. sometimes a project will crash on open etc which somehow makes my hardware loose sync although it still works just with no hardware control page. I hope this helps.