Saving anything redirects to homepage

Hi

Since today, whenever I try to update or save a post or any options within WordPress or uninstall a plugin, I simply get redirected to my homepage and the changes get discarded.

Since this is probably a self-made error, here is what I’ve done today and the last few days:

– 3 days ago (17. Oct) I wrote and published my last blogpost, without any problems.
– Yesterday I setup a new local WordPress installation on my new (one-month-old) Notebook.
– I exported the content from my public Website and attempted to import it to my local installation. I selected that I want all the media aswell and started the import. After it was done, some of the content was there, some wasn’t (I didn’t really care I just wantet some test content).
– I zipped and downloaded my (self-made) theme from my website using cPanel and installed it to my local WP-intallation.
– I changed lots of code in style.css and function.js (locally). None of this code has anything to do with permalinks. The code I changed is about resizing images.
– I updated one of my blogposts on the public website (saw a misspelling).
– Today I changed more code until it worked locally as I wanted it to. I opened cPanel and updated my function.js file with copy-paste. After that I went to my public WP-Backend and tried to update my style.css (Design=>Editor)
– When I hit save I got redirected to my homepage.
– I retried multiple times, without change.
– Finally I updated my style.css with cPanel as I did with function.js.
– After that I realized that this problem occurs pretty much everywhere where I try to write to the database (it seems).
– I updated my style.css and function.js again with cPanel, now it was as it was before I made any changes.
– I tested again, same problem.
– I changed the theme to “Twenty Fifteen”, same problem.
– I disabled all my plugins and tried again, still the same problem.
– I enabled all my plugins again, Jetpack wants me to connect to wordpress.com again, I tried to connect but: “The Jetpack server was unable to communicate with your site domainofmywebsite.com [IXR -32300: transport error: http_request_failed Too many redirects.”
– Since I first got the error I was researching in the Internet, now I read this: https://support.hostgator.com/articles/specialized-help/technical/wordpress/links-on-wordpress-all-redirect-back-to-home-page
My permalink setting was on “post name”, I set it back to default and hit save and it saved!
– I thought “Ok this solution worked for me” and I tried to set the permalink setting back to “post name” and hit save, but I got the same problem again (redirect to homepage), I can’t set the option to “custom” eiher.
– I read somewhere (sorry can’t find the link anymore) that WP Super Cache or similar caching plugins could be the problem. I used WP Super Cache for a few days but it didn’t fit my needs so I deactivated it (but never uninstalled), about 2 weeks ago. Since I didn’t use it anyway I tried to uninstall it but, oh wonder, I got redirected to the homepage, the plugin still installed.
– I can still save posts and edit settings on my local installation.

Here is the list of plugins I use:

– Akismet
– Broken Link Checker
– Jetpack by WordPress.com (German Version: Jetpack von WordPress.com)
– NextScripts: Social Networks Auto-Poster
– TinyMCE Advanced
– WP Super Cache (deactivated)
– Yoast SEO

I really can’t figure out what of the above causes the problem or how I could fix it. I’m glad for any help…

Thank you very much

WcPc