This is a backwards-compatibility break. If your theme or plugin is using some of next action hooks and your are connecting the output between them then take a look a this explanation

Hooks have been called in this order (until this PR):
cmb2_before_form
cmb2_before_{$object_type}_form_{$cmb_id}
cmb2_after_form
cmb2_after_{$object_type}_form_{$cmb_id}

And now they are called at this order:
cmb2_before_form
cmb2_before_{$object_type}_form_{$cmb_id}
cmb2_after_{$object_type}_form_{$cmb_id}
cmb2_after_form

Why? Because this means call this hooks is really dangerous because you could break your html if you expect a relative order, for example, if two plugins using this hooks to print something, the most common workflow is use same relative callbacks (cmb2_before_form and cmb2_after_form) or (cmb2_before_{$object_type}_form_{$cmb_id} and cmb2_after_{$object_type}_form_{$cmb_id})

A visual example with two plugins (Plugin 1 and Plugin 2):
Current order:
cmb2_before_form Plugin 1 opens a div
cmb2_before_{$object_type}_form_{$cmb_id} Plugin 2 prints a p
cmb2_after_form Plugin 1 closes the div
cmb2_after_{$object_type}_form_{$cmb_id} Plugin 2 closes the p

Result:

<div>
<p>
</div>
</p>

New order:
cmb2_before_form Plugin 1 opens a div
cmb2_before_{$object_type}_form_{$cmb_id} Plugin 2 prints a p
cmb2_after_{$object_type}_form_{$cmb_id} Plugin 2 closes the p
cmb2_after_form Plugin 1 closes the div

Result:

<div>
<p>
</p>
</div>