Some of the cars are being heavily modified by CSP car configs, its a very powerful tool, but sometimes the changes that are made by the config file can look off or bad in my eyes. That file may be the cause of the problem if the car is the original Kunos MX5.
Assuming it is the original Kunos car, the License Plate texture is indeed being changed by CSP. take a look in the Car Config file. For me that is located in < C:\Program Files (x86)\Steam\steamapps\common\assettocorsa\extension\config\cars\loaded \_> and the file is < ks_mazda_miata >
This location can actually be located easily from CM in the settings / custom shaders patch / car configs tab, click the three vertical dots in the upper right corner and selecting "view in explorer" option
Comment out or delete this section.
Code:
[INCLUDE: common/materials_license_plate.ini]
[Material_LicensePlate_Europe]
I would guess that the car config the file will need to be edited again if CM downloads an updated version.