The Finn finished 14th after being forced to make a second pitstop for a new front wing, having been well-placed to finish in the points before the problem set in.
"Straight after the pitstop, I started to struggle to the point where I was losing grip, front grip especially," Kovalainen told AUTOSPORT.
"The team found out there was something wrong with the front wing and I was losing more and more downforce so we had to come in and change the nose.
"There is nothing physically wrong with the nose, so they suspect there is some rubber or something stuck somewhere.
"After the nose change, the balance was back to normal and the pace was alright."
Trackside operations director Alan Permane confirmed that the wing was at fault, although the team had yet to isolate exactly what the problem was.
"We don't know what it is, there is nothing obvious but it went away when we changed the wing," said Permane.
"After his first pitstop, you just see it go on the aero data.
"He lost 20 points of front downforce, so we had no choice but to change or he would have gone backwards.
"We put him on the options, put a new front wing on because you never know, if there was a safety car he could do some overtaking later on."
Kovalainen also suffered a KERS failure in his final stint, but was happy with his pace in the closing stages of the race once that was taken into account.
He was also satisfied with his own performance even though the result was not what he had hoped.
"The only other issue was the KERS failed, it switched itself off," said Kovalainen.
"That cost a little bit of performance but towards the end of the race, the pace was right up there.
"But without KERS and with those issues, the result is disappointing, but we've had a good weekend."
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