The random selection of chassis model looks now uses explicit list of allowed looks specified in the looks attribute of the chassis accessory data. If the list does not exist, like it might be case with modded trailers or AI vehicles for previous versions, the first look found in the model will be always used (previously a random look was selected from the looks available in the model). If the vehicle chassis uses lods, the fist look might be different between individual lod models leading to appearance changes when game switches between lods. You should update the definition for all modded vehicles which have more than one look in the chassis.
The large truck dealer prefab did change in similar way to the small prefab in the 1.15 patch. It is now necessary to select the proper variant for the truck branch it represents, regenerate the signs and it might be necessary to do small corrections in its surrounding.