Hi
This is due to a not-really determined issue in the communication between 4SEO and Joomla 4 update key system.
4SEO lets you enter your update key in Configuration | System | Update key. Wehn you do that, we sync it to Joomla storage. If you enter your key using the Joomla 4 user interface, we detect that and sync the key the other, into 4SEo settings, so that the key is always the same in both location.
For a small number of users however, under undetermined circumstances, Joomla 4 erases the key. I have changed the way the syncing is done in recent versions, and that appears to have fixed it. So you should update to version 2.x, then enter again your key and it should stay that way from then.
Let me know if that does not work.
Best regards
Yannick Gaultier
weeblr.com / @weeblr