When posted to forum, some gifs are shown as images / still frames - they aren't moving. User has to click on them to "open" them to see them actually moving.
I'm sorry, but I don't follow you please try to explain using some screenshots. If your question is related to wpForo Advanced Attachments add-on, please open a new support topic on the gVectors forum.
It'd be better if you leave some example URL to allow support members to check the issue.