The Android SDK/NDK upgrades we did a few months ago introduced a bunch of performance problems and we are finally getting a chance to follow up on them. The symptoms were particularly bad on older and low-spec devices like the Jetstream.
The latest beta of Channels for Android (v2021.01.05.0138) contains several improvements. In particular you should see the app boot up more quickly (so you'll see the "Preparing" screen for less time).
Things are still slower than we would like, especially when you have a lot of channels/sources and a lot of recordings/imports. We will continue to make improvements to performance and boot up speed in the coming weeks.