i can confirm the issue. i use wp 5.0.2
yesterday i updated to acf 5.7.9
my custom fields value (for pages) can not be saved anymore.
1. i can select the new value from acf field.
2. my editor page updates accordingly. (js hook works)
3. i publish the changes.
4. the field is not updated. it does not reflect in frontend. if i reload backend page, the value in acf field is set back to the old one.
i do have a custom js hack implemented where i switch some images according to the acf field. this hack still works. so for me its clear that acf has a bug here.
a MAJOR one.