The process of DNS server benchmarks uses things like PING which are unfortunately blocked by some routers, firewalls (software and hardware), as well as a million other things that can go wrong. That's why the issues.
OK, sounds reasonable. But it might then be a good practice to inform the customers in advance what eventually can happen or might go wrong (if possible!).
To prevent people from complaining about errors which aren´t (by design or something else) so to speak.
Kind regards and thanks for your answer,
ngc