If on a reminder it still showes your default stock reminder screen , your phone's calendar software is not compatible.
This happens on a small percentage of phones , were the manufacturer changed the default calendar software.
I'm trying to fix this issue on as much phones as i can.
Please open a support ticket with all information about your phone , and let me know if your phone is rooted.
If you don't know what rooted means, that just means your phone is not rooted.