As I understand it, the problem is the hard limit is 25mb per car (hi.ytf+ytf+ytd+hi.ydt), this is an R* thing, and a quick google shows this has been a problem since 2015 and probably since launch 2013. But car mods have gotten more shiny and with higher quality textures since then. 20mb is just the sweet spot iMalcolm27 recommends, and I try to get around there when adding/replacing cars.
I am curious if it's affected by the number of cars one has as replacements/addons. I don't experience the texture glitch when I only have a few cars added, but in the end I spend more time adding and trying out cars than actually playing the game, and when I'm finally happy and have my whole fleet replaced, bam there goes the textures.
Of course it could just be my old GTX 970 doesn't cut it, I do hear it's humming old CCR tunes every now and then.