This is a known issue with MIDI events other than Volume (CC7) and Pan (CC10). To work around the issue, use the Pencil tool to click in the first control point. After there is at least one MIDI event of the type you are working with, MIDI Draw will behave normally.
Logic Pro X: MIDI Draw control points can‘t be entered on a region
When you use MIDI Draw to add controller data to a MIDI region, it is not possible to insert the first control point.
This document will be updated as more information becomes available.