@David-TP Thank You for Your suggestion. For sure I'll try this and update with results but that's not real/comfortable solution. Yamaha musiccast devices are managed by Musiccast app on smartphone/tablet that needs to be connected to the same network. That means that I would need to switch phone to another network just to control this devices while others like TV, printer are on Home (main) network :D I can live with that but that's not comfortable at all and still there is a question why on E4 all worked fine and on X20 it fails.

Best,

nessip

  @nessip 

A little for myself and anyone reading this thread, educating myself of the concept of IoT Networks, I found this Tp-Link description of IoT. 
 

https://community.tp-link.com/en/home/stories/detail/501928

If I understand the suggested solution correctly, by creating an IoT network for the MusiCast devices it allows them a clear network channel and the ability to stream the music data cleanly without having to share bandwidth with other devices. Furthermore by then removing the Mesh setting for each MusiCast device it forces them to stay connected to a single (pre-selected) wifi point without changing and potential introduction of a data break or pause?

just learning all this stuff as I go.

@David-TP tested...unforuntately the issue persist...I just realized that I forgot to mention that environment is mixed X20 and M5 devices...but still before replacing E4 with X20 there was no problem. Of course I can see significant performance improvement when testing or using laptop or smartphone using x20 but it still doesn't work with MusicCast devices as older E4 did.