Smushing image does not show me the result, it keeps loading (sending) for a long time.

Hello,

When I press smush in media file list or bulk smush, it shows me the sending icon for infinite time. After a while if I refresh the media file list in admin panel it shows "reduce by some_percentage". In bulk smash, it doesn smash a single file.

Is there any server blocking/firewall/port blocking issues related to this? Can you kindly provide any permanent solution for this problem.

Thanks In advance.