If you put in your ~/.Rprofile
options(vimcom.verbose = 4)
then, after <C-X><C-O>, you should get the an output similar to his in R:
VimCom Received: [8] homeuserdirfileRhOfK9sCv8Z7jGpdK5du8cgvimcom:::vim.bol("/tmp/r-plugin-user/GlobalEnvList_homeuserdirfileRhOfK9sCv8Z7jGpdK5du8cg")
vimcom_eval_expr: 'vimcom:::vim.bol("/tmp/r-plugin-user/GlobalEnvList_homeuserdirfileRhOfK9sCv8Z7jGpdK5du8cg")'
The first line is the message sent from Vim to R, and the second one is the command executed by R (the creation of the list of objects in R's workspace).