core: Shelly devices become unavailable for few seconds

The problem

Issue #43432 is not being solved for me.

The Shelly devices becomes unavailable for a few seconds, even after the latest changes that should have fixed the issue.

My setup:

Home Assistant core installed in Docker Shelly devices in a VLAN tagged network. Unifi network devices. Every option suggested in the other issue applied.

What is version of Home Assistant Core has the issue?

core-2021.1.5

What was the last working version of Home Assistant Core?

No response

What type of installation are you running?

Home Assistant Container

Integration causing the issue

Shelly

Link to integration documentation on our website

https://www.home-assistant.io/integrations/shelly/

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