BUG #16691: Autovacuum stops processing certain databases until postgresql rebooted

The following bug has been logged on the website:

Bug reference:      16691
Logged by:          Max Vikharev
Email address:      bm.kinder@gmail.com
PostgreSQL version: 12.3
Operating system:   Ubuntu 16.04.5 LTS
Description:

Hi,

Previously i've reported BUG # 16620. But there is no answer on my new
mails, so i have to open this new report.

Currently we have to restart postgresql 12.3 every 5-7 days to make it  work
properly on 5 terabyte cluster with ~ 50 databases. The problem is that
autovacuum stops to process certain databases and cycles on the only one...
Until we restart cluster. 

We've made a trigger and now detecting very situation when it happen. And it
happen every 5-7 day.
So postgresql is loosing actual statistic, we see not effecttive plans, we
need to restart postgresql and also we have to run vacuum full explicitly
frequently. So this all is huge headake.

Please help us investigate the roots of problem.