Hi,
Our system, put the new answers at the end of the queue, so we don't see them until we answered to the more recent answers.
I bothered to login into the website, done some tests, disabling the massaction plugins (not the system one) allow a fast loading of the page, but once we publish one of the mass action plugins, it is very slow.
So I think that there is an error in one of the plugin which is causing a loop or something like that. We don't have the issue on our end, and when opening a mass action there is no triggers called, so nothing executed. The page load should be as fast in a heavy DB as in a light one.
Maybe a plugin file is corrupted, that's why I asked to update it, more than thant we just released a new version of HikaShop which contains several fixes for the mass action system.
Have you tried to open a mass action on a website with a light DB ?
ps: you answered two months later