I think I solved it by setting the blockingmode to NXDOMAIN, now I get the ERR_NAME_NOT_RESOLVED error as expected and what I am used to work with. Disabling PiHole for 10 seconds lets me refresh and the domain gets loaded as well without any problems like the other error-messages gave me. My Android-phone gives the same error now as expected. When changing blocking mode back to NULL I get the original ERR_ADDRESS_INVALID error which gives problems.
Not entirely sure what this piece of the support-pages means exactly in practice. I'm pretty used to networking and things but I'm feeling pretty stupid now 
This mode is similar to
NULLblocking mode, but experiments suggest that clients may try to resolve blocked domains more often compared toNULLblocking.