The mysterious power surges that vexed BART and many of its riders for several weeks last year may be back.

BART shut down direct service Friday afternoon on the Pittsburg/Bay Point line, forcing riders to transfer to shuttle trains between the North Concord and Pittsburg/Bay Point stations. The disruption occurred after engineers were unable to fix a propulsion problem that surfaced late in the morning, knocking 22 railcars out of service.

“They closely mirror the power overload issues” of early 2016, Jim Allison, a BART spokesman, told The Chronicle. “It’s too soon to say, but there are some similarities.”

Friday’s problem occurred in the same area where power spikes knocked out more than 50 railcars and slowed service for weeks last March and April. Commuters were forced to take shuttle trains and, in some cases, bus bridges to get between the two stations.

“Oh no, not again. It’s always something on this line,” said Shamaila, a Pittsburg/Bay Point-bound passenger riding between the Powell and Montgomery stations Friday evening. She declined to give her last name. “This is going to add 20 minutes to this trip, and I don’t have an extra 20 minutes. It takes too long already. There’s always some problem on the Pittsburg train.”

BART officials said they expected the problems, and the shuttle trains, to last at least through the evening commute.

Last year’s unexplained electrical surges, north of the North Concord/Martinez Station, started March 16 and seemed to vanish in early April as mysteriously as they appeared. The power spikes zapped trains, damaging parts of the propulsion systems and knocking the railcars out of service. Similar electrical problems vexed BART between the West Oakland Station and the Transbay Tube last year.

A special team of experts, from inside and outside BART, searched for the cause of the problems, first looking at trackside equipment that provides power, then examining the cars themselves.

While the problems eventually disappeared on their own, the experts believe that metallic particles, from rails ground by BART crews to reduce noise, may have been the cause. The particles, they think, clung to the underside of BART cars and caused electrical arcing. The issue seemed more likely to occur when the ground was wet and on the uphill climb between the two stations, when the trains are forced to use more power, Allison said.

The agency has since started using vacuum trucks to suck up metallic particles created by rail grinding in the area, he said, as well as picking up debris along the tracks.

BART described Friday’s issues as “trackside equipment problems,” one of several generic terms it uses to explain causes of delays. But when asked by The Chronicle, Allison acknowledged the possible connection to last year’s power surge troubles.

Michael Cabanatuan is a San Francisco Chronicle staff writer. Email: mcabanatuan@sfchronicle.com Twitter: @ctuan