Most likely caused by a pfBlockerNG DNSBL entry to block AWS IPs.
Navigate to Firewall → pfBlockerNG → Reports.
To determine what it being blocked:
Whitelist the following:
device-metrics-us.amazon.com aax-us-iad.amazon.com aan.amazon.com mads.amazon.com #amazon mobile shopping aax-us-iad.amazon.com #amazon mobile shopping aan.amazon.com #amazon mobile shopping
May need to add these, but try each one individually. These are Google ad domains so probably not required.
ad.doubleclick.net googleadservices.com ssl.google-analytics.com s0.2mdn.net
NOTE: pfBlockerNG's DNSBL does not support wildcard domains.
This means that you need to whitelist subdomains individually.