Users still reach the old web server hours after a DNS cutover

At 02:05 the team moved www.example.com from the old host 198.51.100.20 to a new platform at 203.0.113.80 by changing the A record on the authoritative servers. The old host now shows a maintenance page. At 09:10, many staff and customers still land on the maintenance page. Separately, the developers added api.example.com at 09:00 for the mobile app, and QA reports that it "does not exist" from the office, while it resolves from their phones. The change plan did not mention TTLs. Staff use the internal BIND resolver at 10.0.0.53.