hello :)
lets take it from the firewall.
1-now i know you allowed the ip communication but lets see logging,
if it ASA
enable logging and check the dns traffic or if there is any drops it will be logged for you.
2-try to use packet tracer to see the flow if its permitted.
3- packet captures if both options didnt isolate the problem
when you do the pcap make sure to do it for specific traffic and then check exactly what is happening.
