What are the bugs? Is there something not working as it should?
I appreciate this is largely anecdotal at this point, but we put a lot of effort into analysing and reducing Prosody memory usage last year. I've been meaning to tidy the results and publish them with a write-up, but I haven't yet found the time. However the summary is that the GC in 5.2 and 5.3 behaved very poorly for us (even after tweaking the default parameters). 5.1 was somewhat better than these two, but 5.4 has given amazing results (generational mode sadly did not give the improvements we expected, but it was not terrible if I recall correctly).
I guess I'd hate for this performance to be the result of a "bug" ;)
P.S. On a related note, we've experimented with moving our most common/expensive data structures into Rust. So far we've not managed to significantly beat the compactness of standard Lua tables...