Hi Chanin,
I too have found the following issue with DNS cache in this version of code that you are using.
sol14855: The BIG-IP system may incorrectly respond to a recursive query with a non-recursive answer
https://support.f5.com/kb/en-us/solutions/public/14000/800/sol14855.ht
ml
Please let me know if this is the issue that you are currently dealing with.
Looking forward to hearing from you soon.