I’m running the latest version of MainWP. When on the manage plugins page, selecting all sites and searching for inactive plugins only, any time I try to delete a single or multiple plugins (bulk action), they are not deleted. Reviewing the site(s) admin panel directly shows they have not been deleted. We are running on WPEngine platform. In the debug logs, I am receiving and HTTP 200 error for each selected site(s): fetch_url_site:: http status:  err: 
Can you please also check if you are getting the same error when trying to delete inactive themes as well?
I believe that deleting them might be a permission problem caused by WP Engine setup.
I was able to delete both a single inactive theme and multi-selected inactive themes.
I am still unable to delete inactive plugins.
Thank you for the update.
Would you mind opening a private Help Desk ticket so we can collect some additional information & investigate further?