The purpose of the check is to verify the server has survived the previous barrage of queries. This is done by sending a query and checking we get a NOERROR response back.
Previously, that query could've been affected by a servfail cache - the server would return a SERVFAIL answer, thus failing the check, despite being up and running. Use version.bind txt ch query to avoid the interference of servfail cache.
Closes #4117 (closed)