After Maintnance Mode – Sites out of google index

I set the whole website https://www.selbst-st?rkung.at in Maintenance Modus for approx. 2 Month.
After this i lost all my google rankings – ok
But – than i had a look at google search console -> many pages got a Server error and are therefore they are out of the google index. This happens from the moment of usign the Mainenance Plugin. With ongoing time, more and morde pages fall out of the index.
But some pages are still in the index. This cannot be a server error. If i inspect the pages (URL inspect) -> message appears that it can be indexed – set the on list.
This behaviour is since used this Maintenance plugin
Any idea?

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