Hi.
I found a solution for this “problem” it is caused by the readme file for acf-options-page
There is no need to use include_once(‘acf-options-page/acf-options-page.php’); in functions.php
After I removed it the plugin worked fine!
I have the same problem.
I am using my own theme. So there is no other options page add-on declaration.
Fatal error: Cannot redeclare acf_set_options_page_title() (previously declared in /wp-content/plugins/acf-options-page/acf-options-page.php:564) in /wp-content/themes/tam/acf-options-page/acf-options-page.php on line 567
and as you can see the redeclaration is caused by the plugin acf-options-page.php
