Thank you for swift reply.
Given the problem takes place in ~20% of cases it seems the problem is really caused by forcing echo. Since MySensors can cope with 80% of triple messages I believe cutting the number of messages by half would solve the problem. I do not observe issues during presentation though my heaviest node has 9 children.
It also seems to be a better way than engaging in multicast feature.
So the problem becomes more Home Assistant related... Given the ack (Enhaced Shockburst) mechanism, forcing echo seems to be redundant. Instead, the failure of message sending should be reported by the gateway - is there any mechanism possible? I only noticed the send() function returns bool as an advice but did not notice an equivalent returning feedback from gateway via ehternet/serial/mqtt.
The documentation says there is an 'optimistic' option, where "Home Assistant will assume any requested changes (turn on light, open cover) are applied immediately without waiting for feedback from the node", so I believe HA does not require echo.
Unfortunately when trying to set that nothing really changes , and I get the following HA log:
optimistic option for mysensors is deprecated. Please remove optimistic from your configuration file
I will post a suggestion to HA forum to restore this option, unless you know a (good) reason for removing optimistic from HA?