SAP Note 27900 - F1 help

Symptom:

Help returns: No Help information is available

Cause and prerequisites

If a structure was created on a Dictionary structure in ABAP with LIKE or INCLUDE STRUCTURE, and a field of this structure is used in the screen, the Help information from the derived dictionary field is not transferred.
This constellation occurs frequently in conjunction with STEP-LOOP or TABLE-CONTROL (LOOP AT ITAB).
On the other hand, the ABAP list processor is also able to produce the reference to the Dictionary for a field of this type for the Help ID.

Solution
Only use fields from the Dictionary in screens.