They also built their own low-level network protocol based on 0mq. Back when I tried it, it had constant keepalive issues behind NAT and would randomly lose messages (that was in 2014, probably better now).
It wasn't any better as of last year, and its constant connectivity issues were part of the reason I abandoned it.
This is rookie stuff, but it’s a recurring security issue where crypto libraries have APIs littered with footguns. The “lambda x, y, z: None” just strikes me as cargo culting copy paste code - I’m willing to bet there is other software with the same exploit as they all copied the same answer on StackOverflow