SPOnline: Sandox event receiver inconsistent behavior

Question

I have following 3 components:

1. Provider hosted App having full control on web and using App only permissions (App)
2. List-A: This custom list has a sandbox event receiver on item creation. App creates an item in this list (ReceiverA)
3. List-B: This custom list has an event receiver on item creation. ReceiverA creates an item in this list (ReceiverB)

Problem: ReceiverB is not fired in this scenario (ReceiverA fires).

That is, event receiver on List-B is fired if I create an item in List-A manually but not fired if App creates an item in List-A though event receiver on List-A is fired in both cases.

Answer 1

Found the issue here. List-B event receiver is always fired but was throwing an access denied exception when running in context of provider hosted app (it was trying to do more than what app permissions allowed). Due to this it didn't do the intended work and it looked like it was not fired.

Since it is sponline, I couldn't debug the sandbox code. Added logs at each step and put them in a list and that's what helped to figure this out.