This message is saying that for the database index
user_settings_pkey, there are duplicate values of "2, blank, 'filterEditor', 0, and 0" for each respective column in the index.
If there is a relevant entry in bugzilla, it is likely (but not certain) that the action of renaming the
user_settings.assoc_id is taken care of in the 18.104.22.168 upgrade process. (Though since I can't see the bugzilla entry, I can't be sure).
Since in late 2.2.x the
user_settings_pkey only had 4 columns, I assume this error is describing a problem in the data as of the 2.4.8 schema.