Minions do not register anymore

Problem: Minions do not register anymore in ONMS. No Minions appear in the Manage Minions menu. I’ve checked the health status of the Minion and ONMS and both are awesome.
The Minion log is telling me:

16:48:12.331 INFO [Timer-2] Sending heartbeat to Minion with id: minion-name at location: Cloud

which sounds pretty good. That’s why I am assuming the problem is on ONMS side.

Expected outcome:
Minions should register again.

OpenNMS version: 27.0.2

Other relevant data:
OpenNMS was configured to use Kafka and I had 2 Minions that were using it. I’ve reverted the configurations and used the embedded AMQ again, deleted all the old Minion nodes, Minion requisitions and locations and started from scratch. The built-in AMQ is listening on port 61616.

The karaf.log has only some of these entries:

/var/log/opennms/karaf.log.7:2021-02-22T16:55:27,974 | WARN | NettyDnsResolver-NIO-Event-Loop-51-0 | DnsNameResolver | 112 - io.netty.common - 4.1.48.Final | [id: 0x88d4e867, L:/0:0:0:0:0:0:0:0:37981] Received a DNS response with an unknown ID: 22644

and those Telemetry log full of Undeclared field type warnings