According to https://dnsspeedtest.online/ DNS0.EU is usually practically inaccessible (too long response times)
Meanwhile I realized that 86.54.11.13,86.54.11.213 uses HTTP/2 while ROS supports HTTP/1.1 only.
Here you can vote for my FEATURE REQUEST: HTTP/2 support into DoH
I also reported this problem to DNS4EU 5 days ago, no response yet.