Outlook 2016 Won't search

Yesterday morning the search function within Outlook 2016 in Server 2016 worked perfectly. A couple of hours later, the search function quit working with the message, "Outlook cannot perform your search."

I have attempted:

1. Rebuild Outlook Search index
2. Repair Office installation
3. Fresh install Office Suite
4. Rebuild entire system search index
5. Run Outlook in safe mode - Allows basic search functions
6. Disable windows search services
7. Create new outlook profile.

None of these have fixed the issue, except safe mode allowing me to use basic search functions.

What other solutions could be attempted?