Cannot run any Ansible task (related to non-standard ssh port ?)

Problem:

All Ansible tasks stay forever in the queue, do not run

Expected outcome:

Tasks run as expected

Foreman and Proxy versions:
On Foreman server:

root@foreman:/var/log/foreman# dpkg -l | grep foreman
ii foreman 2.0.0-1 amd64 Systems management web interface
ii foreman-cli 2.0.0-1 all metapackage providing hammer CLI for Foreman
ii foreman-debug 2.0.0-1 all provides support utility foreman-debug.
ii foreman-dynflow-sidekiq 2.0.0-1 all package providing dynflow sidekiq services for Foreman
ii foreman-installer 2.0.0-1 all Automated puppet-based installer for The Foreman
ii foreman-postgresql 2.0.0-1 all metapackage providing PostgreSQL dependencies for Foreman
ii foreman-proxy 2.0.0-1 all RESTful proxies for DNS, DHCP, TFTP, and Puppet
ii ruby-foreman-ansible 5.0.1-1 all Foreman Ansible plugin
ii ruby-foreman-deface 1.5.3-1 all Foreman Deface Plugin Dependency
ii ruby-foreman-remote-execution 3.2.1-1 all Foreman Remote Execution Plugin
ii ruby-foreman-remote-execution-core 1.3.0-1 all Foreman remote execution - core bits
ii ruby-foreman-tasks 1.1.1-1 all Tasks management engine for Foreman.
ii ruby-foreman-tasks-core 0.3.4-1 all Foreman tasks - core bits
ii ruby-hammer-cli-foreman 2.0.1-1 all Foreman commands for Hammer
root@foreman:/var/log/foreman# dpkg -l | grep ansible
ii ansible 2.5.1+dfsg-1ubuntu0.1 all Configuration management, deployment, and task execution system
ii ansible-runner 1.4.5-1 all interfaces with Ansible from other systems (Python 2)
ii ruby-foreman-ansible 5.0.1-1 all Foreman Ansible plugin
ii ruby-smart-proxy-ansible 3.0.0-2 all Ansible support for Foreman smart proxy
root@foreman:/var/log/foreman#

whep@devel:~$ dpkg -l | grep foreman
ii foreman-debug 2.0.0-1 all provides support utility foreman-debug.
ii foreman-proxy 2.0.0-1 all RESTful proxies for DNS, DHCP, TFTP, and Puppet
ii ruby-foreman-remote-execution-core 1.3.0-1 all Foreman remote execution - core bits
ii ruby-foreman-tasks-core 0.3.4-1 all Foreman tasks - core bits
whep@devel:~$ dpkg -l | grep ansible
ii ansible 2.5.1+dfsg-1ubuntu0.1 all Configuration management, deployment, and task execution system
ii ruby-smart-proxy-ansible 3.0.0-2 all Ansible support for Foreman smart proxy
Foreman and Proxy plugin versions:

see above

Distribution and version:

Ubuntu 18.04

Other relevant data:

Setup: freshly installed Foreman server. A Ubuntu 18.04 machine is already setup as an Ansible server. So configured it to be a SmartProxy. Remote Execution via ssh plugin works.

But whenever I run an Ansible task, the jobs stays pending and the log of the SmartProxy/Ansible Server show this:

2020-05-19T15:59:34 12dcc320 [I] Finished POST /dynflow/tasks/ with 200 (163.43 ms)
2020-05-19T15:59:34  [D]          Step 337aba16-5889-4580-8737-bb46888aae16: 2   pending >>   running in phase      Run ForemanRemoteExecutionCore::Actions::RunScript
2020-05-19T15:59:34  [D]          Step 337aba16-5889-4580-8737-bb46888aae16: 2   running >> suspended in phase      Run ForemanRemoteExecutionCore::Actions::RunScript
2020-05-19T15:59:34  [D] start runner 4bd79e3c-7e16-42af-8205-f94f46ec4820
2020-05-19T15:59:34  [D] copying script to /var/tmp/foreman-ssh-cmd-4bd79e3c-7e16-42af-8205-f94f46ec4820/script:
  | /root/ansible/playbooks/dummy.yml
2020-05-19T15:59:34  [D] opening session to root@devel
2020-05-19T15:59:34  [D] close: 132.195.124.246:33394
2020-05-19T15:59:34  [E] error while initalizing command Errno::ECONNREFUSED Connection refused - connect(2) for 127.0.1.1:22:
 /usr/lib/ruby/2.5.0/socket.rb:64:in `connect'
/usr/lib/ruby/2.5.0/socket.rb:64:in `connect_internal'
/usr/lib/ruby/2.5.0/socket.rb:137:in `connect'
/usr/lib/ruby/2.5.0/socket.rb:641:in `block in tcp'
/usr/lib/ruby/2.5.0/socket.rb:227:in `each'

SSH is configured on a non-standard port (4812) there!

But it is configured accordingly in the Host configuration (as mentioned: ssh tasks work) and also the job has:

     "ansible_user"=>"whep",
     "ansible_become_method"=>"sudo",
     "ansible_port"=>"4812",
     "ansible_host"=>"devel",
     "ansible_become_user"=>"whep",
     "ansible_become"=>true,
     "ansible_ssh_port"=>"4812",
     "ansible_ssh_user"=>"whep",
     "remote_execution_ssh_port"=>"4812",
     "remote_execution_ssh_user"=>"whep",

Side note: I read somewhere to install ruby-smart-proxy-remote-execution-ssh-core but there are broken dependencies:

sudo apt install ruby-smart-proxy-remote-execution-ssh-core
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 ruby-smart-proxy-remote-execution-ssh-core : Depends: ruby-smart-proxy-dynflow-core (< 0.2.0) but 0.2.4-1 is to be installed
E: Unable to correct problems, you have held broken packages.
whep@devel:~$

whep@devel:~$ cat /etc/apt/sources.list.d/foreman.list
# Ubuntu 18.04 Bionic
deb http://deb.theforeman.org/ bionic 2.0

# Plugins u.a. fuer Ansible Plugin
deb http://deb.theforeman.org/ plugins 2.0

I ran out of ideas, so any hint is appreciated.