After wheelnut issues caused lengthy stops for Valtteri Bottas in Bahrain and Zhou Guanyu in Jeddah, the team made what it called "containment" modifications for Melbourne, with the aim of reducing the risk of further issues.
However, in Melbourne, Bottas suffered another problem on his first pitstop that cost him around 28 seconds and robbed him of a shot at scoring points, as he was running ahead of both Haas drivers at the time.
On the Finn's second pitstop, the wheelnut popped out of the gun and rolled into the fast lane and thus potentially into the path of other cars, which led to a report to the FIA stewards on safety grounds.
After investigating the matter they decreed that "the team lost control of a wheelnut during a pitstop causing a potentially dangerous condition in the pitlane during the race," and imposed the fine.
Although this hadn't occurred on previous occasions Sauber racing director Xevi Pujolar denied that the lost wheelnut was a result of the changes the team has made since Jeddah.
"It shouldn't have happened, but we didn't do any modification that is causing that," he said when asked by Motorsport.com about the latest incident. "What we saw in the free practice and pitstop practice we were reasonably confident that actually today it should be OK."
Pujolar admitted that the recurrence of the problem was very costly for the team.
"From the first race, we found some issues with pitstops, with the cross-thread," he said. "It's something that we don't find when we do free practice, or even during the winter, we didn't find a problem.
"But then every time we go into a race situation it becomes more critical. We took some containment this week, some small modifications. It's not robust enough, and we had one pitstop issue.
"As long as we have this issue, it becomes very difficult for us. It's not the problem with the crew, the crew are doing everything correctly.
"We've got a problem with the hardware, and we need just to make sure that we have got time to find that solution and the parts and we'll try to fix it for Suzuka."
However, Pujolar acknowledged that "the final solution will take a bit longer".
Zhou also suffered a pitstop delay in Australia, but it was due to a gearbox issue that was part of the changes to the driver procedures for the "containment" measures.
