autovacuum is running but pg_stat_all_tables empty

Hi,
I'm trying to understand something that is weird on one of my environments.
When I query pg_stat_all_tables I see that most of the tables dont have any
value in the last_autovacuum/analyze column. In addition the columns
autovacuum_count/analyze_count is set to 0. However, when checking the
logs, I see that on some of those tables autovacuum run. I think that there
is something wrong with the database statistics collector. In addition, the
column n_dead_tup and n_live_tup are set and in some of the cases
n_dead_tup is more then 20% of the table tuples. In addition, all tables
have default vacuum threshold.

Any idea what else I can check ?
The problem isnt only that dead tuples arent deleted (I dont have long
running transaction that might cause it) but the fact that the statistics
arent accurate/wrong.