Working with h-blank interrupt?

[winteriscoming]

Yes please if you have some code to check, it will easier.
Even full code, I'll sign a NDA to keep it secret

Let's start a little smaller.   

The attached code draws a gradient, and even with all the other stuff from my game removed, the gradient still misbehaves on real hardware.

Edit:  I attached even simpler code that exemplifies the issue I'm having.  It has scroll plane 2 segmented into 3 sections.  Some text is printed in the top, middle and bottom.  The middle section moves SCR2_X by 1, and the bottom section moves SCR2_X by 2, so the bottom section scrolls faster than the middle.  The top section stays still.

When the scrolling code is introduced into the hblank in addition to gradient, that's when things misbehave on real hardware.  I can get the gradient working with no issues, if I do only the gradient and forego split scrolling.