Does anyone know if there is a way to detect which line and field was edited on a sublist, when record is updated? I was thinking of going through System Notes of that record, but that wouldn't be too optimal, I think (plus I don't think System Notes records changes to sublists)

You should be able to use oldRecord vs newRecord in user event

Thanks, that's what I do, but still it doesn't seem to be too optimal if you have good amount of items/sublists. I would rather have a list of potential fields to observe, then compare it with data sent to server (I would image it would work like this)

Possible to use a snapshot of the record in a hidden field in before load and then do a compare afterwards. Might be a little faster than traversing the sublists using API