When loading a webform submission by a webform render element to edit, it gets updated immediately on load and on every ajax request.
1. Create a webform
2. Make a submission (insert)
3. Create a route that returns a render array with the webform render element and the submission for edit
// Snippet
$build[] = ['#type' => 'webform', '#webform' => $webform->id(), '#sid' => $submission->id()];
//Full render array
$render = [
'#theme' => 'container',
'#children' => [$build],
'#cache' => ['max-age' => 0],
];
4. Turn on submission logs and watch the "submission updated" operation get triggered along any associated email / handler on initial page load and on any subsequent #ajax request defined on the form elements, no submit button pressed.
This behavior doesn't occur when editing the submission through webform's administration UI.
Closed: works as designed
6.2
Code
After further testing, I found out there was an unrelated hook saving the submission before the route loaded the webform, thus triggering the update operations I was getting. My Bad.