I've been fighting the same issue for over a year.
Jay - I worked with you on June 12, 13, and 14 of 2018 and you had me try:
- download and reinstall
- disable all other add-ins
- sent you a screenshot
- disable antivirus
None worked and the issue persists.
Meir - when it happens, if you open Task Manager, you'll see that Word is still running. Right click and you can select "Bring to Bring" which causes Word to display again. It's a big pain, but a bit of a workaround.