Hi.
Can you email me at [email protected] your WP Admin access details so I could look at this from the inside? Looks like your theme (or some other plugin) is preventing some standard WP hooks from firing and this results in errors you’re having.
Also, have you tried switching to some standard WP theme like Twentyseventeen and see if buttons are working, like Admin advised? This is to test if the problem is caused by your theme.