Alert of Improper disconnect; but HD still connected

I have an older external HD and it is connected via an adapter to my new iMac (USB to USBC); and I am occasionally getting a message that the hard drive was ds
iconnected improperly; but the hard drive is still showing as mounted. Is this due to the adaptor? Will it damage my Hard Drive???

The USB adapter may be preventing the drive to use enough power for operation. You may connect the drive directly to the USB port of another PC to isolate this issue.