A very common cause for DNSSEC validation failure under BIND 9 is firewall issues. Specifically, a firewall that blocks fragments.

To work around this, limiting the packet size one is willing to accept so to avoid fragmentation is a good, but temporary, solution.

options {
  edns-udp-size 1460;
};

This has the side-effect of causing TCP retries on large packets, which are often the DNSKEY responses. However, it also causes DNSSEC to work, so overall it’s a good thing.