Sorry, your session has expired

Yahoo email.  Its always something.

"Sorry, your session has expired. To protect your account, you need to confirm your password periodically."

All of a sudden I'm getting randomly and automatically logged out of Yahoo email. 

Never seen this before, haven't altered any yahoo related settings.

I've searched for answers, but none of the advice seem to be current.  One time when I tried to log bac in it took me to the login page, so I thought maybe coming here someone could give me some advice.

Not blaming Webpage notofier for anything..has been great lately.  

Some have suggested it has something to do with cache or cookies or "keep me signed in" or "sign-in settings" in yahoo that I cannot find.

thx