Network and plugins missing after upgrading new WP version

Hi,
This is a recurring problems and would like to get it sorted once and for all.
I have a WP multisite which works fine. This is until I upgrade a new version of WordPress such as 5.7
When I upgrade I lose the site network option in the My Sites dropdown menu on my dashboard and there is no access to any plugins on any of my sites.
This has been happening for some time and in the past my web host has helped me out but he seems to be stuck this time.
Any help or advice would be welcome.
Thanks
Andy

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