intermittent resolution

[Con Wieland]

I recently upgraded to version: 9.8.6. I am having trouble resolving a .gov site. When I reload the name server it will resolve fine for a while then after an hour or two I will get a server fail. I can perform a dig +trace and resolve but dig will fail. If I do an rndc reload it will work for some period of time again.  I suspect negative caching but the site has a the ttl set to 60 so I would expect it to resolve again but it doesn't until a reload is preformed,  other sites seem to be effected but I don't know. This is a high visibility site. The only configuration change has been to add RPZ which seems to be working fine. 

Other name servers seem to be unaffected. What am I missing? What else can I check? I can provide more details if it would be helpful.

Con Wieland
Office of Information Technology
University of California at Irvine