I've tried using the latest one (RStudio 1.1.447 - Windows Vista/7/8/10) which has exactly the same problem as the one I was using previously. I also tried using one of the latest daily builds and the default resolution of any of those versions (I tried a couple) was very low - I couldn't switch it to my usual 4K resolution, which eventually made using R Studio impossible on my monitor. Not sure what the problem here was exactly.