Undesirable sign out office 365

Hello all
Since a couple of days I have an issue on one of my computers with office 365 / OneDrive
The issue is:
When I start up Excel or Word, I can see that my account is logged in. But....after a few hours, if I open Excel or Word again, I see that I'm still logged in, but if I want to save or print the file, I must sign in again.
Only this computer (out of 3) has this problem.
Anybody?? :-)