Alonso was holding off Mercedes driver Lewis Hamilton for second in the closing stages when he was told by the team to start lifting and coasting, without being given any explanation.
After the race, team principal Mike Krack revealed that Aston's request was triggered by an apparent issue with the fuel system, which turned out to be a false flag.
"We thought we had a problem with the fuel system," Krack said.
"But we were not sure, so as a precaution, we said the best is to save some fuel and to do lift and coast."
When pressed repeatedly by Autosport, Krack refused to disclose any further details on what the erroneous indication was, simply stating: "We thought we had a problem which did not materialise in the end."
By needlessly lifting and coasting, Alonso left laptime on the table but Aston didn't want to take any risk of losing the Spaniard's sixth podium of the season.
"How much it costs us? It's difficult to judge. A few tenths, probably, one or two, maybe," said Krack.
"It was a precautionary thing. But you can choose between not finishing or arriving with a bit more [fuel], so we wanted to be safe."
The Silverstone-based squad's vague instructions to its driver, which Alonso speculated was "to not make me worry too much", also left TV broadcasters and even rival teams speculating about the nature of his troubles.
In the closing stages, Mercedes told Hamilton that Alonso might have been suffering from brake issues, which raised a few smiles on the Aston pitwall.
"I was surprised as well to see the comments," Krack added.
"I think Lewis was told we had a brake issue.
"We looked at each other and said: 'Oh I guess they know more about our car than we do! We should speak to all the Mercedes engineers.'
"But no, we had no problem."
