Are you on WordPress 5.3.0? Are you using Gutenberg or the Classic Editor?
What version of ACF are you using?
I am having this same issue with Gutenberg on 5.3.0 with ACF 5.8.0 Beta3, and I tried a few things to get them to show up again.
1. In Gutenberg, go to Options > Advanced Blocks and see if the names of all your metaboxes are showing up there. Make sure they are all checked. Only two of mine were showing up.
2. Check the DOM to see if they are loading at all. (Inspector)
3. Create a new Admin user account, and go to the page edit with that new account. My issue had to do with permissions somehow, and this made the fields show up for a few hours. But then they all disappeared again.
Reverting back to ACF 5.7.9 fixes everything for me.
