gmail has extra authentication which you have to disable on the gmail side as per Google Gmail | Manager or for Google suite. Changes there by you or google will stop it working. It is designed to required re-authentication intermittently forcing you to re-login to their web interface. Their official reasoning is for security. However if you look at their business model, it also increases the revenue from their product (“free users” screen space and time combined with accurate consumer profiling). So expecting using google services to be easy to use for task which don’t optimize their income is optimistic.
It is possible Manager has a new problem however to track such bugs, a fair amount of detail would be required both on the Manger settings and google protection disabling approach you are using. Also for a Manager problems most people with the same Manager version and same gmail security setting would also be experiencing the issue. Perhaps not obvious initially but should be soon very clear.