A server reaches everything by IP but cannot resolve names after a DNS migration

On Friday the data centre moved its DNS service from 10.0.10.53 (now switched off) to a new pair, 10.0.20.53 and 10.0.20.54. DHCP and netplan were updated. On Monday, deploys on the Ubuntu 22.04 app server SRV1 fail:

SRV1$ curl -sS https://repo.corp.example.com/
curl: (6) Could not resolve host: repo.corp.example.com
SRV1$ ping -c 1 10.0.20.80
64 bytes from 10.0.20.80: icmp_seq=1 ttl=63 time=0.61 ms

Other servers are fine. A colleague says DNS cannot be the problem because ping build01 works on SRV1.