Having this same issue. Also on PC / Steam, using 1660 Ti on Windows 10. Trying to do the NR4 monthly in Monaco. First shakedown everything went fine to the end. Started 2nd shakedown and no engine sound.
Platform: PS4 deluxe edition When competing in any of the "events" (as opposed to free play) my times do not show on the leader boards. Once I complete a stage and see the leader boards, it only shows me the top time. No option to "find me" either. Happens regardless of the event type. However, if I look to see what reward tier I'm in from the main menu, that works ok. I also am still receiving rewards for the ones I complete. The problem does not exist in the free play's time trials.