The F.B.I. mishandled child sexual abuse allegations even after enacting new protocols since its bungled investigation into Lawrence G. Nassar’s assault of young gymnasts, the Justice Department’s watchdog found in a report released on Thursday.

Michael E. Horowitz, the department’s inspector general, found that 42 of 327 sexual abuse cases reviewed were plagued with serious problems — including a lack of coordination with local law enforcement and a failure to follow up on leads — that required immediate attention from the bureau.

The inspector general found “no evidence” that the F.B.I.’s investigators reported instances of sexual abuse to local, state and tribal authorities in roughly half the cases it reviewed. That same issue led to a long delay of an investigation into Mr. Nassar by the bureau’s field offices in Los Angeles and Indianapolis, according to the report.

Mr. Nassar, the former national gymnastics team doctor who is now in prison, abused at least 70 girls and women during that delay, which lasted more than a year. He molested hundreds of his patients, including the Olympic champion Simone Biles, under the guise of medical treatment.

In at least one instance aside from the Nassar case, Mr. Horowitz noted in the latest report, a child continued to be abused by an adult a year after a complaint was made to the bureau.

In 2021, Christopher A. Wray, the F.B.I. director, called the bureau’s failure in the Nassar investigation “inexcusable,” vowing to do “everything in our power to make sure it never happens again.”