hausarzt

Hey folks.
I have a strange problem with one of me self-hosted websites.

Beforehand:
I am not a totaly newbie, when it comes to use and maintain wordpress. I have several sites and during the past years, I have gained pretty good experience in using this cms.

Now here is my problem:
I had a live wordpress site and created a "Staging"-Version of it. I made several changes on the "staging"-instance and everything worked as supposed to be. When all changes were made, I went from "stating" to "live". This process went flawless and the live-site was an exact copy of the staging-site.
I deleted the staging-instance, as everything seemed normal.

After a while I found out, that I can not click the "Save Changes"-Button in all Sub-Menus of the "Settings"-Menu. This includes "General" , "Writing" , "Reading" and so on.
When a Plugin creates a Sub-Menu inside the "Settings"-Menu, this problems occure there as well.
In all other parts of the backend, I can save changes. Only the save buttons in the "settings" menu don't work.

What I have tried so far:
Deactive all plugins
Change user

Before pushing the "staging" to "live", the "Save Changes" Button worked on both instances.

Any thoughts?

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I know, my english is bad. But your german might be even worse