The Factorio devs found[1] that some devices do fail to compute checksums, in that they compute the checksum just fine, but they're doing something stupid with some values and so checksums of 0x0000 or 0xFFFF (the two values from the FFF) cause packet loss.

In any protocol that, when the packet repeats, repeats it with even the slightest permutation (different request ID, timestamp, sequence number, etc.), that will be enough to jiggle the checksum to a new value (probably), and then the protocol will keep going with only a minor blip that probably goes unnoticed.

But if the packet is deterministic, only then you hit the problem.

> calculating the UDP checksum is not exactly rocket science.

I've seen things that trivial get messed up. "Just read the standard" is a high bar, sometimes. (Though the above is probably "I dual purposed a u16 without realizing it didn't have any available niches for that…")

[1]: https://www.factorio.com/blog/post/fff-176

As someone who generally doesn't use AI in software development nor RE, this is one thing that I'd recommend trying one on to see what it can do: the problem is clearly defined and a solution is easily validated, and it's a problem you're not intersted in digging deeper yourself. The other comment here about 0000 and FFFF checksums seems like a good place to start.

A little more digging found this discussion from TODAY regarding what looks like a very similar bug in one of Intel's Linux NIC drivers: https://lkml.org/lkml/2026/5/4/1886

What made it confusing at the time is the join packet would sometimes be accepted and passed through to the game, so it prompted further digging into why.