Problem with the new RopieeXL Version

In my household I have four Raspberry Pi with Ropiee in operation. They have been working flawlessly for several years. There are three Raspberry Pi 3 Model B Plus and one Raspberry Pi 4 Model B. I had only installed RopieeeXL on the Raspberry Pi 4 before.
Now I tried to install the new main version of RopieeXL on all Raspberry Pis manually. I didn’t succeed with two Raspberry Pis 3 and the Raspberry 4. In all cases I could not reach the web interface in the browser. There was always an error message saying the page could not be reached. The Raspberrys were also not displayed in the router menu. Even repeated restarts of the router and the Raspberry did not lead to success. In all cases, the status LED on the Raspberry indicated that the actual software installation was successful.
But then I was able to successfully install the new main version of Ropieee (without XL) on two Raspberry 3. I haven’t changed the third Raspberry Pi 3 yet, I’m running the Raspberry Pi 4 again with the old RopieeXL version.
What am I doing wrong?