Problems updating to version 4.4

Hi,

When updating from version 4.3 to 4.4, the website just stopped presenting any users the message “Briefly unavailable for scheduled maintenance. Check back in a minute.”.

After some 5 minutes I opted to delete the file “.maintenance” and the website coma back to live. But without Yoast SEO at all – there is no entry on the menu, the plugin is not listed on plugin list, nothing.

I have no idea what went wrong or how to start troubleshooting. Can anyone please point me the way to go about this?

Cheers!