Hi @bezerrarodrigo,
We finally found the problem. We have unchecked a checkbox in the BuddyPress settings (cf. screenshot).
We already had a similar problem on our activity wall for another project hosted on WPEngine.. Unchecking this box allowed us to solve the problem.
Note that this issue is not caused by the Gwangi theme. If BuddyPress is unable to post an activity (hosting, misconfiguration, etc.) it doesn’t allow you to do it (and therefore doesn’t do the form reveal animation).
I hope it helped you.
Best regards,