It IS possible to run into "trusted location" issues on your own system even if it is not an external location. However,...
Everything worked fine until two weeks ago.
If it went bonkers on a Wednesday morning, it might well have been an automatic patch because the "Microsoft Patch Model" is for Tuesday afternoon patch distribution and with Win10, those patches can be difficult to stop.
I'm on my old Win7 system so can't find this easily, but if you dig around, you can find a Windows Update Patch History (Google it for Win10) that chronologically (in reverse order) lists patches that your system has endured. You would be able to identify a date for your last patch. It would also give you a KB or other number that you can look up online to see what that patch addressed. If it mentions "trusted location" issues or "file security" issues in relation to Office (any version) then you have a good idea as to what happened. However, without knowing specifically which patch did it to you, a fix would be hard to identify. Though there IS the ability to roll back a patch as a test.