How to debug / investigate non-reproducible build for r-repr?

[Lo Peter]

Dear all,

I am trying to import r-languageserver, and one of its dependency is
r-repr, which I found that cannot be built reproducibly (on my
laptop's guix, installed on Linux Mint), i.e.

        guix build --rounds=2 r-repr

would give the error saying that "...r-repr-1.1.0.drv differs from
previous round".

How should I begin to investigate the issue?

Regards,
Peter