Upgrading from 2.4.1 > 2.5.2 after the upgrade, there seems to be a problem with pulp

Problem:

I’ve upgraded a foreman 2.4.1 (installed as 2.4.0) with Katello 4.0.1 to 2.5.2 according to
Upgrading and Updating Foreman server

I tried to add the required repositories to foreman, to update my (external) smart-proxy to 2.5, too.
However, it said:
There was an issue with the backend service pulp3: Not all necessary pulp workers running at https://foreman-app01-prod.ewsrv.ch/pulp/api/v3.

When I run
foreman-maintain healtch check

I get

Running ForemanMaintain::Scenario::FilteredScenario
================================================================================
Check number of fact names in database:                               [OK]
--------------------------------------------------------------------------------
Check to verify no empty CA cert requests exist:                      [OK]
--------------------------------------------------------------------------------
Check whether all services are running:                               [OK]
--------------------------------------------------------------------------------
Check whether all services are running using the ping call:           [FAIL]
Couldn't connect to the server: undefined method `to_sym' for nil:NilClass
--------------------------------------------------------------------------------
Continue with step [Restart applicable services]?, [y(yes), n(no)] n
Scenario [ForemanMaintain::Scenario::FilteredScenario] failed.                  

The following steps ended up in failing state:

  [server-ping]

Resolve the failed steps and rerun
the command. In case the failures are false positives,
use --whitelist="server-ping"

In /var/log/messages, I also have stuff like this:

Jul 16 15:41:54 foreman systemd[17271]: pulpcore-worker@7.service: Failed to execute command: No such file or directory
Jul 16 15:41:54 foreman systemd[17271]: pulpcore-worker@7.service: Failed at step EXEC spawning /usr/libexec/pulpcore/pulpcore-worker: No such file or directory

For this ping-error, the RH-KB suggest downgrading foreman-maintain, but I’m not sure if that applies here.

Foreman and Proxy versions:
foreman-2.5.2-1.el8.noarch
foreman-installer-2.5.2-1.el8.noarch
foreman-installer-katello-2.5.2-1.el8.noarch

Distribution and version:
CentOS8.4

This is discussed here, apparently:

I didn’t see this when I posted mine…