WordPress is overwriting site titles

Hello everyone,

I am honestly loosing my nerves – I was updating one site when suddenly out from nowhere wordpres started to overwrite the page title. I eerrased the cache – I deactivated every plugin – I updated the template – but I can’t get rid of the problem. and with every try the site becomes more of the same site names . . .

Has someone any idea how to fix that before I throw the mouse out of my closed window?

Thank you very very much!

The page I need help with: [log in to see the link]