making it obvious to users what choices they have .. (Bookmark & Subscribe)

Good idea, you can bookmark post from desktop, mobile and website as well. Yes we have to tell you can get notified by doing that.

when mentioning a user, a list (row) of user names which i can select from no longer appears, yet did before. Now, as i cant remember the exact name of someone i want to mention here, i need to switch to

We have removed it temporary in order to figure out why app is minimizing. And you don't need to switch, https://ecency.com still has that feature, for mobile app we will add back once we find out root cause of this issue.