DNS works everywhere except Building C

Reported: payments.internal returns NXDOMAIN from 10.4.8.0/24 (Building C) only. Everywhere else it resolves. The record was added yesterday at 16:40.

From HQ:

$ dig +short payments.internal
10.0.5.44

From Building C:

$ dig payments.internal
;; status: NXDOMAIN
;; AUTHORITY SECTION:
internal.  10412  IN  SOA  ns1.internal. hostmaster.internal. 2024110402 3600 600 86400 86400

• Building C's /etc/resolv.conf points at 10.4.8.53, a local caching forwarder. HQ points straight at the authoritative servers.
• At 16:10 yesterday (before the record existed), the payments team ran their smoke test from a Building C box. It failed, as expected.
• Restarting the app in Building C changes nothing.