I believe you are right. I think Matthew Flatt mentioned it in one of his more recent talks. Chez scheme didn’t become the default implementation until Racket 8.0 which released Feb 2021 so it took awhile to iron out all the bugs.

They are still in the brainstorming phase and you can look at the issues in this GitHub link https://github.com/racket/rhombus-brainstorming to see what is being discussed

1. https://blog.racket-lang.org/2021/02/racket-v8-0.html