Update:
Unfortunately, we did not manage to successfully complete the maintenance on the test server yesterday and have decided to keep it closed for the time being (until today - 12.05.2021). Since it was infrastructure maintenance, the landing page, i.e. the start page on the test server will remain white.
This is exactly the reason why the server is a "test server", where all situations can be tested, including situations that can then of course be avoided later on the live server.
The test developers are already on it and as soon as we have new information, we will share it with you here.
Until then, we would like to thank you for your fabulous feedback and of course for the error/bug reports.