Cannot turn track_counts on

Hello, all.

I have a Postgres sever with the 'track_counts' setting
stuck in 'off'.  I cannot seem to enable it with either of
  a. ALTER SYSTEM,
  b. ALTER DATABASE,
  c. ALTER USER,
  d. or plain SET.

pg_settings shows:

  name    | track_counts
  setting | on
  source  | override

What does 'override' mean in the 'source' column?  How can I
find where in the system this setting is overridden?

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