ok, it is not the slabs, as your cut occours at 3:10 in your video much before the slabs. It is happening at the 1st actual "broken" asphalt mesh 1BROKEN_00. This is a valid track section as far as Assetto is concerned.
It is possible that RSR only sees 1ROAD_* as valid and should be (IMHO) considered a RSR timimg bug.
View attachment 1193721
update:
Seems it is a known bug as reported by fat-alfie
https://www.racedepartment.com/threads/rsr-live-timing.79007/post-2934339
They are checking dirt+valid track (defaults are ROAD, KERB, GRASS) which is not the proper way they should be doing it
(as I suspected).
They should be also checking for IS_VALID_TRACK=1 in surfaces.ini.
Sorry this is not my issue. (the fix is only to edit the track mesh names and loose the rough tarmac feel/effects)
attatched is a replacement road mesh with the rough spots removed (and kills the track feelings) for you to test and use if you wish.
It will not be included in any future release.