As other people here, i faced the connection time out error with the pygatt integration.
As a more reliable alternative, i found out a homebridge plug-in called homebridge-brewer. So far i have not faced any connection issues.
It looks like it’s using a different bluetooth library to do the job.
In order to use it, you also need homebridge installed.
For hassio, i followed this guide :
https://community.home-assistant.io/t/tutorial-add-homebridge-to-hass-io-using-portainer/140423