lve started to get this issue again, however its happened on my other external as well this time.
l did some googling, and it seems others have had this happen as well, some did mention unknown devices despite everything working fine however from what l gathered the parallel between others issues and my own is it happened while connecting to the front USB..
now l havent actually checked device manager, next time l connect one of my externals and disconnect it l'll have device manager open and see what section refreshes and does the disconnect reconnect thing. its obviously USB related since it only seems to happen when l disconnect one of my external drives.
l might connect a short piece of usb cable to my rear ports and see if it happens on the onboard one.