Leclerc started only seventh after his crash in qualifying, and in a race not impacted by safety cars, he finished in the same position 52.9 seconds behind winner Red Bull's Max Verstappen.
His Ferrari team-mate Carlos Sainz fared little better on his run to fifth, having overcome a five-second penalty for speeding in the pitlane.
Leclerc said it was hard to predict the behaviour of the car not just over a stint but even within a lap.
“I was speaking just now with Carlos and what we are lacking is consistency from the car,” he said when asked by Autosport about his difficult afternoon.
“Not even from corner to corner, just in the same corner I can have a huge oversteery balance and then a huge understeery balance, and our car is so wind-effected.
“This year we have a car that is much more wind sensitive, and we are struggling much more with that. So there is a lot of work going on that.
“Other than that, for some reason this is off because it is not something I have had for the rest of the weekend so we’ll have to check the car, but I had a lot of bottoming especially in high speeds which is something I can’t quite explain, because I didn’t have that yesterday. So this we’ll have a look at in the data.”
Leclerc said the car was just as tricky on both the medium and hard tyre compounds: “It was the same. At the end of the hards once the graining cleared up a bit it was a tiny bit better, but we are just lacking pace and consistency.
“I think it has been similar since the beginning of the season as every single race we are going from one compound to the other and we never know what is going to happen on a new compound, so it is always an unknown how the car is going to react, and if the tyres are going to be in the right window.
“And this is just very difficult as a driver to gain the confidence and adapt your driving, because you go from one set to the other and the car is completely in a different window.”
An extra frustration for Ferrari is that a change of approach for the Australian Grand Prix saw very strong race pace from Sainz, but that now appears to have been a one-off.
“Again, I think this is also part of consistency,” said Leclerc. “We sometimes feel we’ve done a step forward and then you arrive in particular conditions and it is warmer than other races and now we are completely off the right window of the tyres. We need to work on that.”
Ferrari team principal Fred Vasseur acknowledged that it was a difficult afternoon for the Maranello outfit.
“Overall it's a tough weekend and a tough race today because yesterday I think the pace was decent," he said. "But we are not able to put everything together.
“And today it's quite similar, the first stint went pretty well for Carlos, he lost a couple of seconds in the first third of the race, and he lost 25 seconds in the last two-thirds.
"We were far too inconsistent from one car and from one lap to the other. We have to understand why.
“For Charles it was the opposite, he was in a good shape at some stages of the second stint with hards, because he was struggling much more on the first part of the race.”
Vasseur agreed with Leclerc that the inconsistency was the key issue: “We really need to focus attention on this because that is key for us. And where we have to do a step.
“With Charles we were more performant on the hards, with Carlos we were much more performant on the mediums. And even with the same tyres from one lap to the other one we are a bit inconsistent.”
