PG 11.8 > PG 12.3 : Unable to allocate section memory

Hi Community,

We have migrated from postgresql 11.8 to 12.3,unfortunately we have
sometimes the following errors in the logs, causing postgres process to
be killed.

2020-08-12 14:20:29.043 CEST [134644]: [71-1]
user=xx,db=xx,app=[unknown],client=localhost FATAL:  out of memory
2020-08-12 14:20:29.049 CEST [30022]: [6126-1]
user=xx,db=xx,app=[unknown],client=localhost FATAL:  fatal llvm error:
Unable to allocate section memory!
2020-08-12 14:20:29.197 CEST [78792]: [1-1] user=,db=,app=,client=
FATAL:  terminating connection due to administrator command
2020-08-12 14:20:29.197 CEST [78791]: [1-1] user=,db=,app=,client=
FATAL:  terminating connection due to administrator command
2020-08-12 14:20:29.197 CEST [78793]: [1-1] user=,db=,app=,client=
FATAL:  terminating connection due to administrator command
2020-08-12 14:20:29.197 CEST [78790]: [1-1] user=,db=,app=,client=
FATAL:  terminating connection due to administrator command
2020-08-12 14:21:02.621 CEST [86289]: [2-1]
user=postgres,db=template1,app=[unknown],client=[local] FATAL: out of memory
2020-08-12 14:21:04.632 CEST [29597]: [26704-1]
user=xx,db=xx,app=[unknown],client=localhost FATAL:  fatal llvm error:
Unable to allocate section memory!

Here are our settings :

_PG :_

max_connections = 3600

shared_buffers = 32GB
temp_buffers = 16MB
work_mem = 96MB
maintenance_work_mem = 8GB
max_stack_depth = 6MB
dynamic_shared_memory_type = posix

We use postgresql with pgbouncer as a pooler.

_PGbouncer :
_

pooler mode : session
max_client_conn = 6000
default_pool_size = 3000

We have ~ 2000 connections at the same time with ~ 20/30 are active.

Note that we had the same configuration under PG11 without any problem.

Do you have an idea ?

Regards.