Vince, I ran into this issue myself recently while working on the SF sheet. In the repeating section that you have your action button in, do you have a containing div that has a position property applied to it? Something like this (bolded):
HTML
<div class='buffs'>
<!-- contains the buffs repeating section-->
<fieldset class='repeating_section'>
<div class='filter-container'>
<button type='action' name='act_button'>Button</button>
</div>
</fieldset>
</div>CSS
.repcontainer div{
position:relative;
}
Javascript used to test
<script type='text/worker'>
on('clicked:repeating_section:mod', (event)=>{console.log(`clicked:repeating_section:mod event: ${JSON.stringify(event)}`)});//This event will only be triggered if position:relative/absolute is NOT applied to the filter-container div.
on('clicked:mod', (event)=>{console.log(`clicked:mod event: ${JSON.stringify(event)}`)});//This event will only be triggered if position is applied to the filter-container div. However it will not have repeating row info.
</script>
After eliminating code line by line until the events started firing correctly, I found that if you have a div with position:relative or absolute applied to it the event doesn't fire correctly. Position:static doesn't appear to cause the issue, but I have by no means tested all the possible position states. I also have no clue why a css position change would affect how a javascript event is passed since it certainly doesn't affect any other event generation in the sheetworker environment.
