core: MQTT - Timeout waiting for mid

The problem

Updated to 115 beta (same for 0,1,2 betas) and got this error on HA start. MQTT broker - Mosquitto installed on Ubuntu 20.04 (on a different machine in local network).

Environment

• Home Assistant Core release with the issue: 0.115.0b2
• Last working Home Assistant Core release (if known): 0.114.4
• Operating environment (OS/Container/Supervised/Core): Raspbian/Supervised
• Integration causing this issue: MQTT
• Link to integration documentation on our website:

Problem-relevant configuration.yaml

mqtt:
  broker: 192.168.1.30
  port: 1883
  username: !secret mqtt_username
  password: !secret mqtt_password
  keepalive: 60
  discovery: true
  discovery_prefix: homeassistant
  client_id: rpi_ha

Traceback/Error logs

2020-09-09 14:13:02 ERROR (MainThread) [homeassistant.components.mqtt] Timed out waiting for mid 314
2020-09-09 14:13:02 ERROR (MainThread) [homeassistant.components.mqtt] Timed out waiting for mid 315
2020-09-09 14:13:02 ERROR (MainThread) [homeassistant.components.mqtt] Timed out waiting for mid 316
2020-09-09 14:13:02 ERROR (MainThread) [homeassistant.components.mqtt] Timed out waiting for mid 317
2020-09-09 14:13:02 ERROR (MainThread) [homeassistant.components.mqtt] Timed out waiting for mid 318
2020-09-09 14:13:02 ERROR (MainThread) [homeassistant.components.mqtt] Timed out waiting for mid 319
2020-09-09 14:13:02 ERROR (MainThread) [homeassistant.components.mqtt] Timed out waiting for mid 320
2020-09-09 14:13:02 ERROR (MainThread) [homeassistant.components.mqtt] Timed out waiting for mid 321
2020-09-09 14:13:02 ERROR (MainThread) [homeassistant.components.mqtt] Timed out waiting for mid 322
2020-09-09 14:13:02 ERROR (MainThread) [homeassistant.components.mqtt] Timed out waiting for mid 323
2020-09-09 14:13:02 ERROR (MainThread) [homeassistant.components.mqtt] Timed out waiting for mid 324
...
2020-09-09 14:13:02 ERROR (MainThread) [homeassistant.components.mqtt] Timed out waiting for mid 388

Additional information