I have a Western Digital WD Elements 2TB external portable drive that I use for image and system backups on my XP and Win10 systems and don't experience this. Note only my win10 system is on Avast free 19.1.2360, the XP system is on avast 18.5.xxxx as in the info below my posts.
I just use the Safely Remove USB Drive in the system tray/notification area and it takes a few seconds. I do leave it a little while to spin down and then remove it. No corruption or errors experienced.
I would advise not disabling all shields, whilst this may work, it doesn't pin down which shield that has the interaction. I would start with disabling the Behaviour Shield and see if that is the cause, if not, then try disabling the File System Shield.
Have either of you any change to the avast settings ?
If so it might be worth Restoring the factory settings.