I am experiencing this now. Deployed fresh install of SnapCenter 4.0 / vCenter 6.5 U2 / Ontap 9.1P9.
Created a Resource Group and it was visible for a few days, the backup still runs as scheduled - but the Resource Group is no longer visible (it is/was the only one I created). I just created a TEST Resource Group and it too is not visible.
I have three (3) linked vCenters in this environment so regardless of which vSphere web client I log into (yes, it really shouldn't matter but it was worth a shot) I cannot see my (2) Resource Groups.
Another twist... I was once able to see VSC in my vSphere menu but now it is not there when I log into one of the three web clients. I UnRegister/Register the VSC server with the vcenter and VSC is still not a menu option for the one vSphere interface.