Octoprint connection issue JUST with browsers

What is the problem?
I'm getting a time out error ONLY in the browser. Optiprint Anywhere works and I can access the PI from the GUI and see that the IP address is what it should be.

What did you already try to solve it?
Tried various connection settings. It was working fine. Then it stopped. Restarted the Pi to be sure, too. I also tried more than one browser.

Logs (octoprint.log, serial.log or output on terminal tab, browser error console ...)

Additional information about your setup (OctoPrint version, OctoPi version, printer, firmware, browser, operating system, ...) I'm using the latest OctoPi version with an MK3s. Windows 10 64 on Chrome.