The old app had bad layering, and no explicit storage layer. We wanted to experiment with different storage layers, use rx for data flow, switch from java to kotlin, and use all the latest androidx/jetpack best practices. This amounted to a whole new app, and it was easier to start from scratch, despite the disruption to users.
I have to say riotx is miles ahead of riot android. If only it could do voice and video yet.
For desktop I have to say riot has been really on and off. In particular voice/video calls are hit and miss. Sometimes it rings but one can't pick up, sometimes it just does not ring.
I actually have been experimenting with some of the alternative clients (I particularly like nheko reborn) unfortunately non do voice video yet.