It might be possible that even though RKV was built in debug mode, the backing sys crate isn't building LMDB itself this way. On a very first glance it looks like this is the case, always going for opt level 2: https://github.com/danburkert/lmdb-rs/blob/master/lmdb-sys/build.rs#L23
I'll have a closer look at the build process and see what's going on.
Can you share your build process that resulted in LMDB debug functions being optimized away? Did you build using the fuzzer via `cargo afl`? Something else?