Weird problem with new Fritzbox 7590 over wireless - one single device on the wireless network can't get IPs from Pi Hole

I've just upgraded my Fritzbox 7390 to a 7590. After a call to 2degrees to get the settings right internet is working fine for my a variety of Windows 10 PCs, WiFi, all Android phones and tablets.

Next I configured the new Fritz DCHP to hand out the IP of my Pi Hole for ad blocking. This works fine from every PC on Ethernet, my work Surface Laptop 2 over Wifi, my Android 9 phone, my wife's Android 9 phone, my Android 7 tablet on WiFi.

The problem is while my wife's Windows 10 PC can query the Pi Hole over Ethernet to get IPs, it can't get IPs when it's connected via Wifi. It can ping the Pi Hole, ssh to the Pi Hole, and the Pi Hole receives the DNS query, but for some reason the Windows machine doesn't get the reply. I have tried turning the Windows Firewall off, made no difference.

The Fritz is 192.168.1.1 (I changed , the Pi Hole is 192.168.1.11

This shows the problem

nslookup google.com 192.168.1.11Server: piholeAddress: 192.168.1.11

DNS request timed out. timeout was 2 seconds.DNS request timed out. timeout was 2 seconds.DNS request timed out. timeout was 2 seconds.DNS request timed out. timeout was 2 seconds.*** Request to pihole timed-out

nslookup google.com 192.168.1.1Server: fritz.boxAddress: 192.168.1.1

Non-authoritative answer:Name: google.comAddresses: 2001:4860:4802:34::75 216.239.32.117 216.239.36.117 216.239.38.117 216.239.34.117

Here's the corresponding log from the Pi Hole for the first nslookup - I can see the DNS query arrives, but for some reason the PC can't see the reply.

Mar 20 20:05:38 dnsmasq[528]: query[A] example.com from 192.168.1.14Mar 20 20:05:38 dnsmasq[528]: forwarded example.com to 202.37.101.2Mar 20 20:05:38 dnsmasq[528]: forwarded example.com to 202.37.101.1Mar 20 20:05:40 dnsmasq[528]: query[AAAA] example.com from 192.168.1.14Mar 20 20:05:40 dnsmasq[528]: forwarded example.com to 202.37.101.2Mar 20 20:05:40 dnsmasq[528]: forwarded example.com to 202.37.101.1

This works fine on my work PC over Wifi. It works fine on the same laptop over Ethernet. Why is it not working on this one laptop?!

Note that I have hard coded the DNS server to 192.168.1.1 in Windows WiFi properties, so I've got it working, but I'd like to solve the problem :)