The call from the tower PC is a client like I meant it
It shows, that this client uses an IPv6 address as DNS server which is not Pi-hole and not reachable at all.
In general, I see all your clients got GUA addresses (2a02) which are not stable over time and can change e.g. if your ISP delegates a new prefix to your router. If you need IPv6 for your LAN you should use ULA addresses.
If you don't need IPv6, try disabling it and see if blocking works again as expected.
