Stat gpu what this [unaccounted]?

What is [unaccounted] in Stat gpu?
[unaccounted] take 28% in my scane How to fix it?

The document that describes this has vanished from the Epic site, the only information that remains is

GPU work that isn’t explicitly instrumented will be included in a catch-all [unaccounted] stat. If that gets too high, it indicates that some additional SCOPED_GPU_STAT events are needed to account for the missing work.