Hey everyone,
It might be a bit of an amateur question, but I couldn't find a valid solution on Google.
As written in the title, Syntax Highlight and Code Completion features are broke down after the theme change.
I tried to reinstall both R and R studio. I tried to update Rstudio. Resetting Rstudio none of these solutions worked. Checked my settings and all of them are OK. Last thing that I can do is formatting my disk but it's a bit drastic solution so I would like to check other solutions. Attached some screenshots as an example.