Vault closes 2-3 times every day. I don't know why.

I use an online vault.  I open it at every startup, sometimes via the desktop, sometimes my browser (Chrome).  Everything runs as normal, but then suddenly I see that the vault has been closed and not by me.  This has happened twice today and I started up my PC only 3 hours ago. 

Has anyone else had this problem?  Could it be a Windows 10 problem?