Here are some bugs that I faced while using the beta version (android) of Zotero for the past 2 weeks, the bugs are mainly related to the pdf annotations.
1. If I tap on a highlight annotation after creating it, it shows a dialog box where I can change the colour and add note. After closing the dialog box, if I tap on it again it doesn't open the dialog box. I can make it open again after I tap on another annotation and then tap on first annotation again.
2. If I create a highlight annotation of colour B at the end of another highlight annotation of colour A, the recent annotation is merged with the older annotation and is of the same colour. It can be fixed by closing the pdf and then opening it again.

Update:
I recently experienced some more bugs/missing feature so I am updating my post.
3. Annotations made in the PDF viewer in android app take quite some time to be reflected in the desktop viewer. It didn't work even after repeated manual sync.
4. There should be an indicator for highlight annotations that have notes attached to them. This feature is available in the desktop PDF viewer (appears as a small note icon) but missing from the android viewer.