Too frequent 're-log-in' to linux client?

With nextcloud on a linux host, v3.2.3 Ubuntu ‘Impish’, the sync client sometimes appears ‘disconnected’ and requires a ‘re-log in’ on the browser and a ‘re-grant’ of permissions in order to function. The only hint I have is that sometimes I log in on the web interface in other accounts than the user log in account. It is possible the host server got rebooted or communications temporarily lost between the client and host (such as a power-off on the client desktop). But that shouldn’t force me to go through the whole re-login-re-grant steps. What does it take to keep the sync working, open and logged in?