Steps to reproduce the issue

Create a module. Add a repeatable subform(lvl1). Inside this subform add another subform(lvl2).

Expected result

It should load the subforms from lvl1 & lvl2 and save the values from both subforms.

Actual result

It loads alright but it does not save any value from lvl2 or any deeper lvl if you created those (lvl3, 4, 5).

System information (as much as possible)

Latest Joomla, PHP 7.10

Additional comments

This happens whenever you include a subform from the same module and even when you grab them out of another module. Especially with the latest you quickly get into trouble because whenever you pick a module that already has a subform init then it won't work. Which I believe one of the reason the subform was created in the first place.

Don't get me wrong I love the subform and the functionality but I also think that nested subforms should work!

Stackoverflow Issue

I created a SO issue before I posted in here: https://joomla.stackexchange.com/questions/18285/joomla-3-6-nested-subforms-not-saving

It might hold some more valuable information.