Does this also happen when using http://pi.hole/admin ?
The recent pihole-FTL v5.9 extended interface-dependent handling of pi.hole and the machine’s hostname, enabling Pi-hole to reply with different addresses on different interfaces (as opposed to handling only the configured interface as before).
Starting with the most recent pihole-FTL v5.10, you can control how Pi-hole will reply with an address for which a local interface exists, by appropriately configuring PIHOLE_PTR in your /etc/pihole/pihole-FTL.conf.