@Pepe also user from Turris 1.x eth2 driver problem thread had same issue and actually same solution, so i assume its affect every 1.x router. But as issue is self-healing within a few seconds you typically not paying attention to it (or blaming ISP). I actually started to debug it once i had a quarantine and had a lot of zoom meetings from home 
Anyway, thank you for all your work, marking problem as solved. As a bonus with TOS6 DSA vlans are working as expected now.