I just wanted to report that there is a conflict of some kind between Activity Plus and the BP GTM plugin by SlaFFik. Whenever GTM is activated, Activity Plus just stops working. While on the surface it appears that the issue may be with GTM, but one never knows so I'm asking for a dev here to investigate to see if there is anything in Activity Plus that contributes to the issue.
It's been reported in the WP support forums and I sent SlaFFik an email from his contact page tonight. BP GTM is also due for an update to be compatible with WP 3.5 so hopefully he'll get a chance to take a look soon.
Reporting here because I think it is good practice to report conflicts to both parties whenever plugins are involved.