I have done the same, dropping down to Personal when my plan renews later this month, as I do not consider the Professional cost to be valuable for my use requirements.
Apologies I tested Notebooks which is working.
Never tried with Stacks as i have no need i only have one Stack and it is already in alphabetical order as i would like it to be.
I just got the whole page Tasks yesterday. All my recurring Tasks (many of which were created when recurring tasks was introduced) are all displayed correctly in the Tasks Page & Widgets on both Desktop & Mobile.