What causes the order qty to be zero and grayed out in the Scheduling Agreement

Hello Experts,

Could you please answer the below queries on the Forecast delivery schedule tab (Scheduling Agreement)?

(i) What causes the order qty to be zero and grayed out in the Forecast delivery schedule tab (Scheduling Agreement)?
(ii) If the order qty is zero, how come the system shows confirmed qty?
(iii) How should I delete or block these grayed out schedule lines?
(iv) How to check who added these schedule lines in the agreement?

Below are the VBEP details for all the schedules (just for reference)

Thank you!