I do not have such issues on my end so I do not know honestly. I recall that some plugins can bring such issues : few years ago ENBseries was included because it gives the best image IMO but drawback is that ALT-TAB is broken and fps are no more smooth.
About borderless I suggest you to ask either to @Shovas or @Bjarne Hansen as they both use a tiny soft which I do not recall the exact name (borderless gaming or something like that).
Moreover GTR2 engine is old and does not like the recent high polygons conversions from rf2/AC : these games can use 16Gb RAM but not GTR2 so these high polygons cars can make image stuttering and can lead to freeze or even CTD at some point so in this case try to reduce grid to only few opponents (10-20).
About borderless I suggest you to ask either to @Shovas or @Bjarne Hansen as they both use a tiny soft which I do not recall the exact name (borderless gaming or something like that).
Moreover GTR2 engine is old and does not like the recent high polygons conversions from rf2/AC : these games can use 16Gb RAM but not GTR2 so these high polygons cars can make image stuttering and can lead to freeze or even CTD at some point so in this case try to reduce grid to only few opponents (10-20).