What's going on?

[silverback]

I'm hoping someone can help me understand what's happening on my Windows 10 PC.
Occasionally, I get a warning triangle on any office application (as per the photo).
You can see what the message says when I click on the triangle.(Photo1)
The implication is that it isn't my Microsoft account, because the Microsoft portion of the message offers a Sign Out.
But if I click on the Sign In link in the Account Error portion, I'm offered a Microsoft login - apparently.(photo2)
I'm seeking help on why this keeps happening. I'm not doing anything unusual and subscription for Office 365 is 8 months hence.
Thanks
Silverback

[JoeP]

Have you changed anything in your networking recently?

Have you tried to repair your Office installation?

[StuartR]

This happens to me when I run ccleaner, you just need to log in again

[silverback]

Have you changed anything in your networking recently?

Have you tried to repair your Office installation?

No and No.
However, I have run CCleaner as Stuart posits. I shall log in again, and keep an eye on whenever I run CCleaner again.

Thanks, people
Silverback

[HansV]

In CCleaner, select Custom Clean. In the Applications tab, clear the check box for Office nnn.