Current status:
The search works now with an acceptable speed (i.e. searching for MarkDown needs around 10 sec for getting results, but when I try to get more information about a result, by clicking into e.g. ThiefMD, nothing happens at all for several minutes. There is no hint that it is working. I gave up after several minutes (having switched between AppCenter and FireFox (typing this message here). When I guess correctly that I can find ThiefMD under the topic work and scroll down the list manually the detailed info about ThiefMD pops up with a reasonable delay.
So there is still room for improvement.