I have noticed a recurring issue for the past few months that sometimes when I create/load variables, they do not show up in the Environment viewer. The variables themselves are still accessible as usual, and using the remove() function on them works as expected as well. Refreshing the environment viewer does not help, but recreating/reloading the variables or restarting the session does sometimes; though it often takes multiple tries.
I'm using RStudio version 1.4.1717, with R version 4.1.0, on Windows.