If you want to migrate existing Peak sites to Statamic 3.3, in addition to the Runtime parser please change the following.
Control panel forms now only submit visible fields
From the Statamic Docs:
Control Panel forms now only submit visible fields (as originally intended) which fixes `sometimes` / `required_if` / etc. validation rules, among other things. This could potentially be a breaking change if you were using field conditions purely for cosmetic showing/hiding of form fields.
The button fieldset in Peak relied on this unintended use of conditionally hiding fields. To fix this replace your (vanilla) Peak button fieldset (
resources/fieldsets/button.yaml) with this updated fileopen in new window.