mahdiyazdani Sorry, I haven't logged in the forum here for a while, so I am not sure if my reply is still helpful for you.
That plugin was developed for a forum that I am maintaining (<https://d.cosx.org/>, in Chinese), and it seems to work well on the website. The forum system has already been updated to beta 7.1, and I don't see apparent problems for the gravatar. Let me know if you still need help on this issue.