I select: Debug > On Error > Error Inspector
Effect:
It works great for two or three times, but then it goes back to just printing an error.
Great. It started working again without having made any changes to the configuration. It should work a few more times before reverting to error messages again.
It's hard to say. Setting the error inspector effectively does something like:
options(error = <RStudio error inspector>)
which implies that any R code executed that changes the error handler could mess up this feature. Are you able to find any action, or set of R code, which reproducibly seems to turn off the RStudio error inspector?
No. However, everything I am using is within the Tidyverse and none of my code calls options. Whatever it is, it apparently turns it on and off seemingly randomly. There are other reports of this in the Internet that can be found using Google.com.