Cursor selects multiple items

When I am logged onto my office by anydesk, randomly, the mouse cursor selects multiple items. Nothing I do from the remote computer fixes the issue. When I go into the office to fix this, it appears to be the right shift key causing the problem. As soon as I touch the right shift key, the problem is fixed. I thought it was the office keyboard so I cleaned the shift key in case it was sticking. No change, the problem persisted. I then purchased a new keyboard and replaced it for the office keyboard. No change, the problem persisted. If it is not the physical keyboard in the office or the remote computer, what can cause this? How can it be fixed?