That's probably a sympton of the 7135, the worse 7135's don't do well at low PWM's. In my 16X XHP50 light, the low PWM's work fine in lighting up all 16 LED's. I'm working right now on a similar setup - the MT03, 3 XHP70.2's and this driver: https://budgetlightforum.com/t/-/40540/67.