Statistics tables not being updated anymore

Hi.

v9.6.9

Statistics views like pg_stat_*_tables, pg_stat_*_indexes, pg_statio_*_tables and pg_statio_*_indexes aren't being updated anymore. Specifically, all counter fields are 0, and date fields are blank.

The first thing I checked was postgresql.conf (but it hasn't been modified since December 2018), and track_activities is turned on. Also, I connect as user "postgres", so it's not a privileges problem.

Where else should I look?

track_activities                    | on           

track_activity_query_size           | 1024         

track_commit_timestamp              | off          

track_counts                        | on           

track_functions                     | none         

track_io_timing                     | off          

Thanks