Why Wemos D1 ESP8266, ioBroker (Raspberry Pi 3 Model B) MQTT connection failed?

Question

Raspberry Pi

I have a Raspbery Pi 3 with ioBroker as an MQTT broker and a Wemos D1 ESP 8266 with a test script. Both devices are connected to the network via Wi-Fi.
Good news:
1) I can send an MQTT signal from my phone (myMQTT apps) and it shows up in IOBroker logs (phone is connected to wifi).
I can send an MQTT signal from my laptop.
Can send successful MQTT signal from Debian virtual server to vmware.
2) Wemos D1 successfully connects to the test server test.mosquitto.org.
Bad news:
Wemos D1 won't connect to ioBroker on LAN and reports "Attempting MQTT connection...failed, rc=-2 try again in 5 seconds" error.
Why are all devices successfully connected to the mqtt broker except Wemos D1 ESP 8266?
Could it be a firewall issue?
Please tell me what should I do to solve this problem.