Paragraphs & OH: Additional slot row disappears after value change when used in nested paragraphs

I have some questions about your patch.
- the patch is not against latest version, with for example part of 📌 Refactor the JavaScript for the widget to use the once library Needs work in it. That is not a problem however to evaluate your patch. But it does already introduce some more focussing.
- you have a problem in a specific paragraphs constellation. I presume you have no problem in a less complex layout? (there were some issues with paragraphs before)
- in the first 2 parts, I guess the addClass/removeClass is the part that truely fixes your problem?
- in the first 2 parts you change the UX: removing the cleared row and adding the 'Add' link of the previous row. I guess that is not part of your problem, but an additional feature? Indeed , current behaviour is more like 'clear', then 'remove'. But I feel removing the clicked-upon row is confusing.
- in the last 2 parts, why do you switch from 'id' to 'data-drupal-selector'? Is that best practice? If so, I can change it, but it gives no technical/functional improvement, does it?

Additionally, please check the introduction of once in #3449164-11: Refactor the JavaScript for the widget to use the once library → , if it will not break your use case.
I need some confirmation on the proposed change there.

Please find the remainder of your original patch, for the hide and once features.