The flying checkpoints also need a line on the track

[Some guy in europe]

I'm playing that boost gate challenge and it's annoying to anticipate exactly at what point you have to be boosting. It would be better if there were lines on the track so you can clearly see when it has to be active.

[Coxatris]

The gates match up with where you need to be boosting. Lines on the ground would be a positive, but I think that might not be your problem.

You only count as boosting when the word "boost" is flashing. Orange and Pink boosts last for several seconds and there are sections where you need to use an Orange/Pink boost to get credit for a checkpoint that's down a straight path far away from a turn.

Several things end a boost early and some things stop it from starting entirely (even though you get a slight animation and the sound for starting a boost). Hitting the brakes, driving in the grass/dirt on the edge of the track, running into a wall and running off the track will all end your boost early. Attempting to start a boost while touching the edge of the track will also result in no boost occurring. It's quite hard to get a clean run on some of the later tracks.

[Jet Uppercut]

You only count as boosting when you're above your car's base top speed (red part of the speedometer). So just pick a car with low speed and high power like Krissi's and you'll be clearing these challenges in one shot since she's basically always counted as boosting if you're above 230km/h.