I'm pretty sure this is exactly the same visual bug which we've always experienced. Even before the L30 update, drivers would max out at L19 unless you trained them correctly.
To get a driver to reach Level 30 you must train all attributes EXCEPT ONE to 30. Stop training when only one attribute remains at 29 (usually one of the Mental attributes). Now continue racing the driver and wait until the Experience attribute reaches 30. Once this has happened, resume training so that the one attribute you left at 29 also goes to 30. When this happens the driver should also jump to L30.
Don't worry if your overall driver level is less than 30. Providing all of the attributes are 30 and they have Green BMI they will perform exactly the same as a L30 driver, it's just a visual bug.
