Strange behaviour going on. A minute ago, my phone suddenly resolved koffiezetapparaat.lan properly. I wanted to make some screenshots to show you this along with the current settings (for future readers ofr future reference) but all of a sudden, koffiezetapparaat.lan does not get resolved properly anymore.
Luckily, I saved the tcpdump log (as pwned suggested). I will read through this and try to find out what went different this time.
Correct resolving:
16:02:02.808623 ARP, Request who-has koffiezetapparaat tell Telefoon.lan, length 46
16:02:02.808802 IP Telefoon.lan.18456 > openwrt.lan.53: 40623+ PTR? 190.1.168.192.in-addr.arpa. (44)
No resolving:
16:13:32.611251 IP Telefoon.lan.59676 > 52.232.216.86.443: Flags [P.], seq 2606:3587, ack 5756, win 422, options [nop,nop,TS val 819405971 ecr 1053534868], length 981
16:13:33.400697 IP Telefoon.lan.59676 > 52.232.216.86.443: Flags [.], ack 6064, win 433, options [nop,nop,TS val 819406768 ecr 1053543441], length 0
16:16:01.132239 IP Telefoon.lan.49108 > 20.185.73.23.443: Flags [P.], seq 3588:4569, ack 6064, win 433, options [nop,nop,TS val 3457205215 ecr 710600902], length 981
16:16:01.305224 IP Telefoon.lan.49108 > 20.185.73.23.443: Flags [.], ack 6372, win 444, options [nop,nop,TS val 3457205401 ecr 710608801], length 0
16:20:24.274708 IP Telefoon.lan.35954 > 20.44.78.251.443: Flags [.], seq 2030808332:2030809760, ack 3394053553, win 422, options [nop,nop,TS val 1762652882 ecr 3877128620], length 1428
16:20:24.274838 IP Telefoon.lan.35954 > 20.44.78.251.443: Flags [P.], seq 1428:1580, ack 1, win 422, options [nop,nop,TS val 1762652882 ecr 3877128620], length 152
16:20:24.939723 IP Telefoon.lan.35954 > 20.44.78.251.443: Flags [.], ack 309, win 433, options [nop,nop,TS val 1762653551 ecr 3877139229], length 0
What I think is happening here: Android maybe uses a range of different DNS (over HTTPS) servers to resolve hostnames. The one time it resolved koffiezetapparaat.lan correctly was the time that it used a blocked Google DNS server and thus relayed it to openwrt.lan to do the resolving. The other times, it gets passed as HTTPS traffic to different IP's.