Postgres logging_collector probably blocks auto_explain output Postgres 10.4

Postgres 9.6

Problem on both versions

I want to collect postgresql slow queries plan, so I added to my postgresql.conf setting from documentation 

session_preload_libraries = 'auto_explain'

auto_explain.log_min_duration = '5s'


in the end of config

But also we use 

logging_collector = true


and if logging_collector is on, no explain in logs

If logging_collector commented, I can see plan of queries
How can I use both options?

UPDATE: 
We had about 10 queries runs more than 5 seconds, but finally with grep we found only one output in log with explain instead of all plans
How it could be only one record was logged? neither all plans, no no plans only one explain
Works for me.

Could it be that the other long queries were run over existing connections (perhaps with a connection pooler) for which the session_preload_libraries has not taken effect?