Previous bug report of major version is https://bugs.gentoo.org/show_bug.cgi?id=616436 A new minor version was announced 2017-06-30 (see https://stat.ethz.ch/pipermail/r-announce/2017/000616.html). Bumped locally and have used for a week without any issues.
Thank you for your report
=dev-lang/R-3.4.1 is now in Portage.