scrape_partial_errors counts up but no errors in log

[mozai]

What I tried:
prometheus-process-exporter -debug -once-to-stdout-delay 1s

What I saw:

• error getting proc ID for pid 820804: open /proc/820804/stat: no such file or directory
  namedprocess_scrape_partial_errors 617

What I expected:

• error getting proc ID for pid 820804: open /proc/820804/stat: no such file or directory
  namedprocess_scrape_partial_errors 1

Each time a scrape is done, I might see one error message; sometimes none, but scrape_partial_errors goes increases by hundreds when there's only about 600 processes total on the machine; with a config file that has five matchers the counter could increase by thousands without any errors in the -debug log. I'd like to know what are these partial-errors so I can address them.