Datahub 1811 not reading sendername and senderport with Error using fallBackHttpDestination

[Private_Member_578813]

Hello everyone,
we are currently in the process of migrating Datahub to version 1811 (and 1905 after).
We have stumbled upon an old problem from
https://answers.sap.com/questions/12763484/no-saplogicalsystem-found-with-key-%27sap000%27.html and
https://answers.sap.com/questions/12762082/sapidocoutboundadaptersendername-in-localpropertie.html

Namely we get the following error in the Datahub log:

10:26:43,908 [DEBUG] [DefaultIDocOutboundAdapter] Sending 2 IDocs to ERP
10:26:43,913 [WARN] [DefaultIDocOutboundAdapter] Error reading HttpDestination, using fallBackHttpDestination instead.
IDocTargetSystemNotFoundException: No SAPLogicalSystem with defaultLogicalSystem=true found in pool=DataHubPoolEntity{id=9300, name=SAPCONFIGURATION_POOL}

IDocs from registration in the hybris shop currently have the following header:

edi_DC40=ADR3MAS03.IDOC.EDI_DC40[
[...]
sndpor=
sndprt=LS
sndprn=
rcvpor=
rcvprt=LS
rcvprn=
[...]
]

BEFORE migration it looked like this:

edi_DC40=ADR3MAS03.IDOC.EDI_DC40[
[...]
sndpor=HYBRIS
sndprt=LS
sndprn=HYBRISQAS
rcvpor=MEQCLNT100
rcvprt=LS
rcvprn=MEQCLNT100
[...]
]

You will note that both receiver and sender data and not filled in with the fallbackhttpdestination.
We do have the following properties configured:

in local.properties for the Datahub:
sapidocoutboundadapter.sendername=HYBRISQAS
sapidocoutboundadapter.senderport=HYBRIS

For the hybris 1811 Backoffice SAPGlobalConfiguration.sapLogicalSystemGlobalConfig (what you see in the Backend-Connectivity Tab):
sapLogicalSystemName=MEQCLNT100
sapHTTPDestination=<configured SAPHTTPDestination>
sapSystemType=SAP ERP (is this a problem if the customer supposedly migrated to S/4 at the beginning of the year ?)
senderName=HYBRISQAS
senderPort=HYBRIS
defaultLogicalSystem=true

Right now neither of the values takes a hold when sending the registration.
Does anyone have a solution for this problem or maybe an idea why they are not being used?

Thanks in advance and regards!

Andreas