In AMQ7, "protocol CORE not found in map: [AMQP]" ERROR

Issue

I have a mesh cluster of two brokers. Everything is working fine if three protocols CORE, OPENWIRE and AMQP are running on the same port 61616 configured in the acceptor. The cluster is also established on this port.
The problem arises when AMQP runs on another port 61620 and a second cluster connection is configured on this second port.
As soon as the second broker is started, it logs the following ERROR:

ERROR [org.apache.activemq.artemis.core.server] AMQ224096: Error setting up connection from /xxxxx:xxx to /yyyyy:61620; protocol CORE not found in map: [AMQP]

xxxxx is the IP of the first started broker.
Why isn't it possible to run a cluster with each protocol op a different port?