Setup:
OD Version: 7.2 (7.2.1.0502) Build id: 201802120814
Prompt & Collect node.
I do not explicitly set the terminating character to "#", since I understood this is the default.
Grammar attached.

I want to enter 8,9 or 11 characters, terminated by the #.

Works with the following entries:
8 chars, no term char
9 chars, no term char
8 chars + term char
9 chars + term char
11 chars

For entry of 11 chars + term char, it works differently.
I get the 11 chars for the current node but the # is sent as input to the next Prompt & Collect node, therefore satisfying the next input.

Why do you need the pound in the grammar? If you mean # to be the termination char, you don't need # in the grammar. Have you tried not having # in the grammar? Are you testing on the platform? The simulation may not work consistently.

I assumed I need all characters I want recognized in the grammar. I guess that was my misconception.
I will try removing it.

I am testing on real platform, not simulator.

I will respond with my results.
Thank you