Hello,
Try to disable Massive Addons plugin, if this solves the 404 problem, you faced a known issue of the Massive Addons plugin that caused by server limits https://codecanyon.net/item/massive-addons-for-visual-composer/14429839/comments?page=36&filter=all#comment_14143143 https://codecanyon.net/item/massive-addons-for-visual-composer/14429839/comments?filter=all&page=79#comment_18501820 You need to contact hosting provider and ask to increase the maximum body length value, then you will be able to edit pages.
Registration for plugins is not obligatory – https://xstore.helpscoutdocs.com/article/38-activation-and-purchase-codes This article will help you to update plugins – https://xstore.helpscoutdocs.com/article/37-plugins-update
Regards
