The bias was unexpectedly sent fully to the front, causing the American driver to lock up and slide into a run-off area at Turn 4.
After initially believing that he would have to retire, Sargeant was able to drive back to the pits and resumed after swapping to a new steering wheel. The change appeared to address the problem, but he eventually finished a distant 20th.
"With Logan, we have an uncommanded brake bias movement all the way to the front, which is why he went off," Vowles told Autosport. "The brake bias moved nowhere near where he requested it to be."
Sargeant admitted he couldn't comprehend what was happening when he first had the issue.
"It was just doing things on its own without my asking," he said. "I don't completely understand it from my side.
"We've had some electronic issues the last couple of days, qualifying and then today. So we just need to understand the core issue. We thought we fixed it, but obviously it came back.
"It didn't happen again, once we changed the steering wheel, so maybe it's something there. But we just need to understand the core cause for it, and try to not let it happen again."
Both Sargeant and his team-mate Alex Albon also had to deal with unexpected power unit temperature problems during the race, which Vowles insisted disguised "a much faster car".
Having qualified 13th, Albon was told that his Mercedes engine was running too hot almost from the start of the race, a problem that was shared by the works cars but not by fellow HPP customers Aston Martin and McLaren.
Albon had to not only manage the issue but also had to deal with the distraction of a high-temperature warning that dominated his dashboard, making it harder for him to undertake any adjustments that were requested by the pitwall.
He eventually finished 15th, but Vowles is adamant that with a clean race, Albon could have led the chase of the top five teams that dominated the points positions.
"I know that we have a much faster car than that," he said. "The fortune is only - and I shouldn't be thinking this way - in the fact that our direct rivals didn't score points either. So it became a nullified race through circumstance.
"There were many things that just weren't in the right place. First and foremost, you would have seen that we were suffering with engine temperatures from lap 2.
"That's unusual. You can often have engine temperature issues, but normally manifest themselves a little bit later than that. We need to get on top of understanding that, that was very, very costly.
"So you didn't see what we can perform with. I think the field is very tight. I think we have the potential to be P11. But not to be in the points, to be clear. We have work to do to get there."
Albon admitted it was hard to draw too many conclusions from his pace in the race, given the compromises, but he conceded that there was some promise.
"I think the only stint you can actually take from our race was the first stint, kind of, in which we actually showed quite good pace," he said.
"I felt like I could extend my stint quite nicely. The final stint I was in clean air, but everything else was just driving around a second slower than I should have been."
