kolloquia.de can't be reached via 1&1 DSL connection

At least since 0930 this morning (2022-11-10) kolloquia.de cannot be reached via the German 1&1 DSL network. Again and again the same problem! As far as I know 1&1 uses the infrastructure of the German Telekom, our biggest communication services provider. kolloquia.de itself is hosted by Host Europe, a company which is part of the GoDaddy network of Internet companies. To me it is a mystery how such problems can occur over and over again without anybody fixing it once and for all!

Of course, I've contacted the support and gave the all the necessary information, but I have no hope that they will come up with any findings. My goodness...