Hi Cerstin,
It is possible that several users access the collection at the same time and run different queries. [...] From time to time (I cannot see a specific pattern), they report a time-out.
Did you choose a timeout in BaseX? If no, what's the message you‘re getting from the server/browser? Did you try the latest version?..
http://files.basex.org/releases/latest/
The result for a query is a HTML code with checkboxes, the rendering of each element is done within XQuery. Perhaps this makes the whole process too slow and the browser times out waiting for the results?
I assume that most time is needed for retrieving the actual results. If you don't want to list all 2000-4000 hits, you may reduce them with a position filter, e.g. (...)[position() = 1 to 10].
Hope this helps, Christian