Desktop shows mobile menu in admin

[cpx3]

First all the best for 2026, may it be a Processwire year!

I have quite a strange problem: from one second to the other the admin shows only the mobile navigation on the desktop but not the desktop version. It happens in all browsers, I cleared the cache, the cookies, tried all versions of different UIs but nothing seems to help. Any idea what could be wrong? 

Thanks,

Bernhard

[maximus]

Hello! Which browser your use ? more details if possible

[cpx3]

Safari, Firefox, Chrome... But it is only one particular site that makes problems, all others are fine. I tried to switch the Ui theme but with no success