The Scuderia was tipped as the favourite to win by several of its rivals going into the Montreal weekend but in low-grip conditions, both Charles Leclerc and Carlos Sainz failed to advance to the top-10 shootout in qualifying.
From there, a wet-to-dry race still provided both drivers plenty of opportunities to move up, but that didn't happen either.
Leclerc suffered a crippling engine issue from lap 2 onwards that saw him pit to reset his car and eventually lose a lap before ultimately retiring from the race.
Sainz suffered early damage to his front wing and floor after contact with Sauber's Valtteri Bottas and while he finally found some pace on slick tyres as the track dried up, he spun out on a wet patch at Turn 6, taking Williams' Alex Albon with him.
Amid a "long list" of issues, Vasseur admitted "everything went wrong" for the Scuderia in Canada, with Leclerc's power unit issue that left him down 80bhp the most frustrating problem on the day.
"With Charles, on lap two we lost part of the power," Vasseur explained.
"We were expecting a red flag to do a power cycle and to try and come back but the red flag never happened.
"It was not just the engine itself; I think it is the control of the engine that we had to stop the engine completely. We went through a cycle but it was 30 or 40 seconds.
"For Charles, when you are in the car, fighting in a group and see you are missing 10 or 15 kp/h, you have no chance to overtake, your engineer is telling you you are missing 80 horsepower, I can perfectly understand that motivation is difficult to find in this kind of situation.
"If he was not frustrated in these conditions, I would be worried."
Sainz equally endured a frustrating afternoon after being unable to move up for long spells of the race before he retired.
But the main damage was done in qualifying, in which Leclerc and Sainz qualified 11th and 12th respectively.
Vasseur said the team has a better idea of why it couldn't find speed in damp, low-grip conditions, and was much more optimistic about its race pace on Sunday before disaster struck.
"The pace was strong on Friday. Conditions were tricky [on Saturday] a and a couple of cars had the same issue - I won't go deep into details - but we were quite confident for the [race] pace," he explained.
"The issues in the beginning... everything went wrong and I hope we have put all the shitty parts of the season on the same weekend."
But with Mercedes now seemingly making it a four-way fight at the front, putting an ever bigger emphasis on race weekend execution, Vasseur said the team isn't going to overreact or change its usual approach that has seen it start the 2024 in strong shape.
Asked if it was his most difficult weekend in charge of the Maranello squad, he said: "The most difficult? I don't know but it was not the best one.
"Sometimes you get the feeling everything is going wrong and going against you but we don't change the approach.
"We are working as a team with the drivers in the good and bad moments and we will keep the same approach for next weekend and continue together.
"I'm not [bothered] at all by this kind of weekend, it is what it is."
