The exercises are too difficult!
The French exercises, particularly the gerund timed exercises, are much more difficult than their Spanish, Italian and Portuguese counterparts. The statements are esoteric and too long for the time allowed
okay, to see what you mean, I went and did those exercises. They certainly are not simple. Here is an example: "On ne peut pas être heureux en ayant peur de tout" (one can not be happy while being afraid of everything) – and that is one of the simpler ones.
It seems the sticky point in many of them might be the verb "avoir", (ayant) and if that is the case, you can practice avoir, that should make the rest easier. I'm just guessing here. The sentences certainly were knotted!