These issues are being worked on by Nick Roberts, Stephen Dolan and Damien Doligez
I think you meant Nick Barnes and not Nick Roberts.
There have been several reports over at GitHub - ocaml/ocaml: The core OCaml system: compilers, runtime system, base libraries
See issues tagged with performance:
GitHub · Where software is built. A number of these are to do with memory regression.
The core team has been working to upstream the first of the major fixes. The first one is the Mark Delay PR ("Mark-delay" performance improvement to major GC by NickBarnes · Pull Request #13580 · ocaml/ocaml · GitHub), which is close to the finish line. A number of smaller PRs for GC pacing improvements should follow next. I’m hoping that we will get these regressions fixed in 5.5.