I am not seeing this error, the issue is not in ACF.
WP automatically adds wp_ajax_ to run the action, this is not something that is supplied on the client side.
Please ensure that you have error logging turned on https://wordpress.org/documentation/article/debugging-in-wordpress/
Deactivate other plugins to see if you can figure out what is interfering. Also check your theme if it is not another plugin. If this fails then try uninstalling and reinstalling ACF, you might have a corrupted file.
