Vault prompt outside of browser

With some regularity and starting sometime during the past year, when I boot up or wake my computer, I get this box on my screen. Sometimes I get two of them. No browser is open. If I click on cancel or just X the box, it goes away. If I do enter my vault password, again, it just goes away. I have detected nothing happening in either case. Why am I getting this prompt? It never occurs during a session, only upon boot up or waking.

 

Vault Prompt.jpg