Mercedes team principal Toto Wolff has conceded Lewis Hamilton was faced with balance issues during the second day of running at F1's Bahrain pre-season test.
The seven-time world champion finished the morning session eighth fastest with 72 laps to his name before handing over the W14 to George Russell for the second session.
Hamilton was confined to the garage for repairs after shedding bodywork but was able to recover to complete his run plan.
But it seems that whilst Mercedes' porpoising issues have vanished with the new machinery, there are other issues at hand that have hampered the team's progress on the second day of testing.
Car out of balance
"The car is out of balance this morning, and you can see that, when driving, it's leaving black marks on acceleration," said Wolff.
"It's hot, and we just didn't find the right setup for these conditions, which I guess is part of the learning with a new car.
"It's not because the driver is over-driving the tyres or pushing, it's the car that doesn't give you enough grip from the rear.
"This is something we need to sort out over the course of today."