I'm aware that the reference below points to generated code, and the culprit is whereever this code gets generated.

SonarQube correctly criticizes the approach as unnecessarily slow.

What should it do:

• replace the longest prefix that ends in either / or \ by empty string.

What it really does:

• the right thing, as above, but then also:
• for each character position of the remaining base filename try to find another / or \
  that means if the basename has 100 characters it will try to re-match the regexp on 99 starting points.

My suggestion is to change the generator itself, such that the referenced line gets created that way, instead:

return filename.replaceFirst("^.*[/\\\\]", "");

I hope it makes sense and that others more into the codebase will find the relevant template or generating location instantly...