404 messages on pages

I am using moderno as a theme and have created a child theme of it. I randomly get a 404 message on most of my pages or it doesn’t display any of the content within the page except from the header.(I have not made any changes to these pages) When I change the theme I am using from the child theme to the original then change it straight back to to the child theme it fixes the problem and I can see everything (no 404 message). I was wondering why this keeps happening and what a possible permanent solution would be? Thanks in advance for the help. 🙂