Why when using two bridged MQTT brokers, Zigbee2Mqtt devices go offline?

I will try my best to explain the whole situation and hopefully it won’t be too confusing.

I have Home Assistant OS installed on my local server together with the Mosquitto MQTT broker and I am also running Zigbee2mqtt.

What I was trying to do:

I wanted to add another, this time external (online) mqtt broker and bridge it together with my local one, so I can communicate with devices outside my network. I did this following this guide and it worked.

What went wrong:

After setting everything up, I checked my dashboard and saw all of my Zigbee devices Unavailable, checked Z2M dashboard and all devices were there and online, I could control them and everything.

I cannot find a solution online and could not figure it out on my own, so maybe someone here who is more knowledgably could help me out.

My /share/mosquitto/mosquitto.conf file:

connection hivemq
address [adress]:8883
remote_clientid hassio
remote_username [username]
remote_password [password]
start_type automatic
bridge_cafile /share/mosquitto/isrgrootx1.pem
cleansession true
try_private false
bridge_insecure false
topic # in 0

Mosquitto broker configuration:

logins: []
require_certificate: false
certfile: fullchain.pem
keyfile: privkey.pem
customize:
  active: true
  folder: mosquitto

Restarting the Zigbee2MQTT addon fixed it!