Are you using the browser on an Android phone to log in to an e-service with Smart-ID and when you return to the browser after opening the Smart-ID app, your browser session has timed out and your login cannot be completed?
Most common reason is that the “don’t keep activities” option has been activated in the Developer Options menu.
NB! Developer Options, sometimes named “Developer Settings”, is semi-hidden on some phones and you might need to do an internet search to find instructions on how to access it for your specific phone model.
Most people will find Developer Options through “Settings -> General -> Developer Settings” or through “Settings -> System > Developer Options” or through “Settings -> About Phone -> Software -> Build Number”, in which case you will need to fast-tap 7 times on Build Number to open it.
Once you’ve opened Developer Options, locate “Don’t keep activities” and turn it off.