Hi @Thibaut_VINCHON ,
please see Posting code? Read this first! for some tips regarding code formatting on the forum.
The first thing I would suggest is to try with a more recent ROOT version, possibly v6.26.02. You can run it from a docker container, or from an LCG release, or install it as a conda/snap/homebrew package, see Installing ROOT - ROOT .
If the problem is still present in a recent ROOT version, please share the CSV file with us so that we can take a look.
Cheers,
Enrico