Mercedes' sudden recurrence of its severe porpoising issues in Miami Grand Prix qualifying left the team "confused" and with the situation "not making a lot of sense", according to George Russell.
The British driver sparked hope the Silver Arrows had overcome its early-season woes and was finally in a position to at least take the challenge to Ferrari and Red Bull around the Miami International Autrodrome by finishing top of Friday's running.
The W13 seemed a more settled machine with the addition of a new front wing, rear wing and beam wing aimed at solving some of the team's issues.
Yet optimism of a pole challenge faded to a disappointing 12th on the grid for Russell as the aggressive porpoising returned.
Speaking at the end of the session, he conceded: "We are a bit confused to be honest. My qualifying lap was slower than the lap I did in FP2.
"The car felt completely different, we struggled a lot with the porpoising and just couldn't attack any of the corners really.
"It is a real shame because I think there was the potential in there and we saw yesterday we were really quick and it has massively gone away from us. Don't really know why."
Mercedes porpoising "inconsistent"
After starting to experience issues in the final practice session ahead of qualifying, Mercedes reverted to a safer set-up that would normally counteract the porpoising problem.
But explaining the complications involved in trying to eradicate the hindrance, Russell revealed: "It is just a bit inconsistent, to be honest.
"We thought we went pretty conservative with the set-up to make sure we avoided any porpoising but it seemed just as bad as we saw in FP3.
"It was going all the way through the corners in turn four, turn five and you just can't attack the braking zones.
"It is not making a lot of sense at the moment and when we get in the window it is fast but just a bit disappointed for myself and for the team. The potential was there."