Confirmed, dnsmasq stalls at
#0 0x00007ffff7b15700 in __read_nocancel () at ../sysdeps/unix/syscall-template.S:84
#1 0x0000555555566533 in read_write (fd=fd@entry=13, packet=packet@entry=0x7fffffffe334 "\002[\001", size=size@entry=1, rw=rw@entry=1) at util.c:654
#2 0x000055555557029c in tcp_request (confd=13, now=1523191598, local_addr=0x7fffffffe410, netmask=..., auth_dns=0) at forward.c:1713
#3 0x0000555555575999 in check_dns_listeners (now=1523191598) at dnsmasq.c:1745
#4 0x000055555555d019 in main (argc=<optimized out>, argv=<optimized out>) at dnsmasq.c:1061
I will contact Simon Kelly about it - I'm afraid there will be no quick solution to this... Please don't use DoH meanwhile!