I've only ever used Collabora via the CODE server on my nextcloud instance, which has worked without issues on both desktop and mobile. Though that obviusly isn't accessible without setup, or when offline, even.

Is there an issue tracker for Collabora somewhere? Are these problems known?

If not, reporting your problems is step one towards getting them fixed. I'm not really finding alternatives either, so that will likely be faster than waiting for a whole nother FOSS office suite app to pop up.