Might be another app causing the problem (if 1 app has bugs it can prevent others working), try disabling all the apps you use from the menu and then turning them back on. I checked that it works in 1.3 including 64 bit version.
Go into the app folder: Should be something like C:\Program Files (x86)\Steam\steamapps\common\assettocorsa\apps\python\stereo_odometer\
Open odometers.txt
In the [Adjustments] section, delete the line of the car with the problem (ks_alfa_romeo_155_v6) and the app will recalibrate next time you drive the car.
Works best in the latest version, but to be safe, take it easy the first time you drive the car - accelerate smoothly to about 100km/h or when you see the odometer adjust itself.
An excellent and very well crafted idea.
For me one of the best game app.
Odometer I consider that it should have all cars games ...
tested and funaciona great.