Considering the domain being distributed systems, and aiming to implement "a Rust-based multi-Paxos consensus engine that not only implements all the features of Azure’s Replicated State Library (RSL)", I don't think we even have to look so deep into it, it's severely lacking tests.

If you're building a distributed system and you don't have more tests and testing code than actual code, by an order of magnitude most likely, then you're missing test coverage.