Upgrade to WP 5.8

Hi
After upgrade to 5.8, the widget’s created under “Simple Page Sidebars” cannot be maintained anymore (appearance/widget/add or change a widget to a sidebar) – the layout is changed – widgets on the left dispaear, sidebars still displayed but incomplete.
When try to create new entry, only the WP blocks can be selected, but not those from origin “Simple Page Sidebars”
When I set the cursor to the blank areas, where the origin “sidebar widgets” are hidden,
it is possible to do some changes – but it’s very limitated.
I could replay this behavior in my old xammp – WP prototype where i did upgrade also to WP 5.8 (w/o touching the other plugins)
I’m using WP theme fourteen
Can you have a look on this issue?
Thank you very much
Kind regards, Rolf

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