Hi @Vlado and thanks for your message.
The purpose of these changes is to build a webmail service for the future, and to expand it with essential services like calendaring (which we have long promised to do).
The current trend shows that progressive web apps (PWAs) will continue to increase in popularity compared to native apps, and with Runbox 7 we are at the forefront of this development.
Our efforts are aimed at increasing Runbox’ competitiveness in a market that’s seeing rapid development on several fronts, and we believe that this will benefit our customers both in the short and long term.
We appreciate any and all feedback on the Runbox 7 project, and invite everyone to comment on the Runbox 7 Roadmap and get involved to help shape the development. 
Regarding the screenshot you posted we have had intermittent issues recently with a backend service which is used by both Runbox 6 and Runbox 7, so this doesn’t really reflect the stability of the Runbox 7 webmail itself.
– Geir