Signatures no longer working

Since the last update, my signatures are no longer functioning. When I select signatures in a new email window, it does not list any - it is simply blank, the divider bar, and then the menu option to open the Signature editing panel:

Then, once in the Signature editing panel, only my signatures for my exchange-based email account appear. Otherwise, all of my email accounts appear when I click the drop-down menu to select a different (IMAP/Gmail) account, but when I select any of the non-exchange email accounts, it shows "Accounts are not available.":

If I then click on the drop-down again, it opens a pop-up window stating "This option is available only when Microsoft Outlook is running. Do you want to start Outlook?"

Regardless of if I select either Yes or No, nothing happens.

Clearly, Outlook is already running, I am using Outlook to test this stuff. My signatures are there in the appdata folder as well, so it is not an issue of missing signatures either.

The steps I have attempted to resolve:

• delete and remake signatures
• run Outlook in safe mode
• fully uninstall and reinstall office
• delete all accounts, fully uninstalling and reinstalling office, and then adding the accounts again

This issue only started occurring earlier this week. So, is this just a beta issue, or is my office/outlook just completely broken?