I have the latest version of BuddyPress. The latest version of WordPress and the latest version of ActivityPlus. They are running on the latest version of the Weaver II Theme. After hours and hours of work, from pulling out other plugins, reinstalling the Weaver theme, the last option is here.
As the administrator of the group, I am able to post a single new item in a group, whether it is a link, photo, or media. Additional posts are not displayed. In some cases, I have attempted to repost the same link again, not thinking it has posted, and didn't see it. Gone to another browser, and then see it. Or looked in the RSS option and found every copy of the post, but still see no posts whatever in the group page.
There are no caching plugins installed, and its at a big host, so likely not a memory issue.