Maybe (hopefully not) but at least in the case of this specific error, it’s because ACFE’s checkbox renderer hooks into acf/render_field/type=checkbox, so it’s trying to access internal properties that ACF appears to have locked down in 6.5.0
I ended up patching the checkbox class as a temporary fix since it’s the only place I’ve come across the issue (so far) – hopefully the dev will push a proper update soon. It’s been a while since they did, though :/
If you know PHP, the class you’d need to patch is in pro/includes/fields/field-checkbox.php – I added local properties for $values and $all_checked, then switched the reads/writes from $instance->values/all_checked (in the render_field, render_field_toggle, and walk functions) to use those instead (except for render_field_custom which still needs/works with $instance).
I would post the full edit, but it’s rushed monkeycode on a pro field class, so I have to assume the dev wouldn’t be cool with it.
