It's a corner case of ordinary traffic, since all TCP apps and most UDP apps adapt to PMTU, but fragmentation is there for those that don't. It's not like something you can only get by generating malicious traffic intentionally.

Welcome to networking mistakes, I guess. I can't remember the specifics but I once encountered a router that would drop traffic that looked like encapsulated TCP at a certain offset, or something like that. They couldn't fix it because the behavior was hardwired. I knew of it because I worked with the firmware team.

Factorio discovered that UDP packets with a checksum of 0x0000 get dropped by some devices.