Comment 14 for bug 1961697

It's definitely non-deterministic, unfortunately. I do have a reliable reproduction for Bionic and Focal I can trigger on my laptop, but it's a huge pile of proprietary Ruby code that just happens to hit all the right timings on my machine. I can validate a -proposed package if you need though.

The reproduction instructions basically boil down to "Have IPv6, call getaddrinfo(), and if you're unlucky, it will take > 5 seconds and make 4 DNS queries instead of two".

There is also a test case provided in the upstream glibc patch that could also be applied.

https://sourceware.org/git/?p=glibc.git;a=blob;f=resolv/tst-resolv-txnid-collision.c;h=611d37362f3e5e89b92766f0790459340cc071b3;hb=2dfa659a66f20facc4082207884c20e986ddecee