Specifically, see the problems shown for the r-devel Debian checks.
These can be reproduced by checking with --as-cran using a very current
r-devel (r77865 or later), which makes data.frame() and read.table() use
a stringsAsFactors = FALSE default, which is planned to become the new
default for the upcoming R 4.0.0.
From the CRAN message:
Please see the problems shown on https://cran.r-project.org/web/checks/check_results_fst.html.
Specifically, see the problems shown for the r-devel Debian checks.
These can be reproduced by checking with --as-cran using a very current r-devel (r77865 or later), which makes data.frame() and read.table() use a stringsAsFactors = FALSE default, which is planned to become the new default for the upcoming R 4.0.0.
Please see https://developer.r-project.org/Blog/public/2020/02/16/stringsasfactors/index.html for more information about this change.