For the second day in a row, the 18-year-old gave his team an early finish.
He did just 12 laps on Tuesday before spinning into the gravel and damaging a new front wing that the team had no replacement for.
The broken one was sent back to the factory, fixed and brought back by private jet, and Stroll did 98 laps on Wednesday before putting the car in the tyre wall and giving the team another headache.
"There was an issue on the car and I was kind of a victim of the situation," Stroll told reporters long after nightfall at the Circuit de Catalunya following an extended debrief with engineers.
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"We are still figuring it all out. What happened, happened and that’s it."
The new crop of cars, with bigger tyres and more downforce, are harder to drive than last year's and considerably faster through the corners, some of which can now be taken flat out.
Nico Rosberg, Hamilton's ex-Mercedes team mate who retired after winning the world title last season, said the changes would turn drivers into gladiators and some might struggle to cope physically.
Hamilton said it was a tough time to be a rookie.
"I feel for him (Stroll) in the sense that it is the toughest year to come into Formula One, being that these are the fastest and most physical cars and such a short amount of testing," the Briton told reporters.
"I know he has been driving around the world testing in the Williams team, so he has definitely had more preparation time than any other driver coming in would have had," he added.
The Canadian, who won last year's European Formula Three title and whose father Lawrence is a billionaire, has tested older Formula One cars as part of a programme to get him ready.
"Last year's car is easy compared to this year's car," said Hamilton.
"These are only the first days and you can't just jump in and drive from no experience at all to being consistent. It is actually good for him to go through this now rather than at the first race."
Williams's head of performance engineering Rob Smedley said there was no blame being directed at Stroll and the team would do their best to test on Thursday, although that remained uncertain.
(Editing by Ed Osmond)
