In fact it is not. Main branch last analysis on 8.2 was on Wednesday, June 3, 2020 2:06:35.989 PM, so only 15 days after PR branch update_date.
I then ran again Main branch analysis but post 8.4 upgrade. And as the 8.4 upgrade did modify all updated_at fields of the database then dbcleaner process would not find this PR branch still suitable for purge…
We’ll check back in 30 days see if things are evolving correctly