I've recently had to do some changes and modify the ESXi management IP address. Once the ESXi host has been put to maintenance mode and removed from vCenter Server inventory I've updated the DNS server records: A and PTR records. Checking DNS resolution works, I've tried to re-add servers to vCenter Server using their FQDN, but it errored with no route to host. This is because of the DNS client cache on VCSA.
To solve it fast and not wait too long you need to ssh to VCSA appliance and run the following commands:
systemctl restart dnsmasq
systemctl restart systemd-resolved
Once the services are restarted you can add again the ESXi hosts using the FQDN.