What about saving your data to SD-card or computer and reflash? This may not be the most expert advice, but maybe the fastest way to get back a working device.
There was a bug that made e.g. Slack icon disappear after install and reboot iirc. I think you should open a separate regression bug report about that. (Then again, X runs Android 4.4 support, which doesn’t get updated anymore, so…)
Known issue; most likely due to OOM situation. There’s a button for it in Sailfish Utilities. (Reboot fixes it, too.)
Downgrading isn’t supported, so re-flashing is the only reliable method to achieve that.
Happened to me also Xperia 10III no tone on incoming call and no sound when calling. reboot fixed. But this has been an issue in many models so maybe it is time to fix this bug. I am 70 and it freaks out my daughter when I do not answer. Luckily the light comes on so one can see eventually that someone has called.