Difference between R.3.4.4 and R.3.5.1 in R API for C
I found a solution (thanks to Luke Tierney on R-devel mailing list).I just needed to move the call to Rf_endEmbeddedR to the destructor of RManager, where it should have been.
It doesn't really explain why it worked the way it was before with R.3.4 and not with R.3.5, but it does solve the practical issue.Maybe this was never supposed to work with Rf_endEmbeddedR called so soon, and it only used to, thanks to a bug that has been fixed.