can not edit or create an event

Hello I use event calendar with the theme avada. Since a few days I try to add or modify events. and it’s impossible. there is no error message. I update my change and nothing. and when i want to see the preview, i have a 404 error. i have version 4.9.3.1 and the latest version of WordPress. Avada support explained that it did not come from them because there are the same mistakes with a basic wp theme. I activated the debug box but does not register anywhere. I updated wp time zone data and events and still not able to update where to create a new event. I even tested with “UTC”. I deleted the plugin by taking reinstall and it took the events but still impossible to edit or add an event. I also checked if everything is checked in themefusion and it’s ok. there I confess that I do not know what to do … I searched everywhere but nothing. so i hope someone can help me … avada misguided with my ftp settings. Is there a problem waiting for a fix right now? thank you in advance if anyone can help me Chris