I recently updated to polymode and poly-R versions 0.2. I am running Aquamacs 3.5 on MacOS 10.14.6 Mojave. When I open an R buffer, as soon as I click on the menu bar, Aquamacs immediately crashes. I have replicated this on two different computers.
I traced the problem to the (easy-menu-define poly-markdown+R-menu) function in poly-R.el. If I comment out lines 218-225, and byte-compile the modified file, the crash goes away. I'm not sure what functionality I am losing, so I don't want to submit a pull request just yet. But there appears to be an issue with that function.