I noticed this some time ago, today tested the new 488 DLC and happened again. I did race with 20 AI GTE cars, and 1 Porsche 911 RSR (and Aston Martin too) had blank skin. You can see that even windscreen wiper is white.
you probably have some out of date skins that were in place prior to most of the latest PBR shader updates that began a year or so ago. If you have ever used the old SIMTEK GT3 mod, that may contain out of date skins as well. One car may be causing conflicts with others. I've loaded two GTE/LMP2 sessions without any of those issues, so I don't think it's the current DLC that is causing the problem.
Check you rcd files here's one of mine which works ok for with latest updates. The lines which may cause problems I have indicated, only change the lines I have indicated the other lines are not relevant to you. Check all you rcd files for the Aston and Porsche. It's usually one of these lines which is cause the white cars Aston Martin. //[[gMa1.002f (c)2016 ]] [[ ]] GTE (If different change to this) { Alan_Harvey { Team = DCA Racing Component = AstonMartin_Vantage_GTE_2019 (If different change to this) Skin = DCAalt.dds VehFile = 28_AMV_GTE8EE6638B.VEH (If different change to this) Description = DCA Racing - Alan_Harvey Number = 99 Aggression = 48.96 Speed = 91.67 QualifySpeed = 96.35 WetSpeed = 85.42 StartSkill = 90.10 Crash = 8.85 CompletedLaps = 91.15 MinRacingSkill = 91.67 Composure = 85.94 } } Porsche. //[[gMa1.002f (c)2016 ]] [[ ]] GTE (If different change to this) { Alex Davison { Team = Gulf Racing Component = Porsche_991RSR_GTE_2017 (If different change to this) Skin = 18WEC86alt.dds VehFile = ENKEY36112E9CDB.VEH (If different change to this) Description = Gulf Racing - Alex Davison Aggression = 44.27 Speed = 83.33 QualifySpeed = 88.02 WetSpeed = 86.46 StartSkill = 85.94 Crash = 5.21 CompletedLaps = 88.02 MinRacingSkill = 86.46 Composure = 84.90 } }