If the hub you have commented on and want to share is in your feed there are two buttons below your comment. One is 'preview' and the other is 'share.' Click the share.
Only one other person I know of has complained that the share button has disappeared. It is still there for me when I comment on somebody's hub or respond to comments on my own hubs.
One other possibility is that it may be your own computer. Every now and then I have to restart my computer because embedded videos on hubs don't appear, or sometimes comments don't show up in my feed, or other weirdness happens. It isn't necessarily your computer, but it doesn't hurt to restart it just in case that will fix it.
If you try restarting your computer and it doesn't resolve the issue, write to team members and let them know. Peggy W is having the same problem and there may be others. If it's happening to a lot of hubbers then HP should be notified.
Hope something here will be of help to you.