Hi, 

Same problem here. Using on-prem instance, Tokyo patch, with Next Experience UI. 

gilde.ui.session_timeout value is set to 60 

Still users get "session expired, please log in again" -pop-up about every 5 minutes after being inactive in instance. Weird thing about this is, that after this pop-up, user really don't even have to log-in again, just needs to close a pop up from X and continue working. 

Consulting ServiceNow support from this.

Bug maybe?