It might have been due to either https://github.com/rust-lang/rust/pull/31319 or an LLVM upgrade. But stuff like looking at the values of basic integer types, the fields of structs, tuple fields, thin pointers, and even many enums works fine. You just have to make sure you have debug info enabled.

Keep in mind std in the Rust distribution was built without debuginfo, so if you step into functions from that, things don't work too well.