Ann: Mukuyu-2 Drilling Update, page-127

"So they need to lower the mud pressure a bit, now that the mud system is working properly"

Where you're taking mud losses and pumping LCM (lost circulation material) isn't working you would then look at other solutions which would include dropping mud weight. However how far you can safely drop mud weight is dictated by formation pressure and frac gradient for the whole open hole section not just the thief zone. You also need to be aware of any effect a lower mudweight might have on borehole wall stability.

The ASX report doesn't give much detail on the severity if the losses but the overall time taken to reach current depth suggests that they got on top of the losses with LCM reasonably quickly and didn't spend an excessive amount of time dealing with the losses.

As Ive noted already where you have a thief zone in a well you would sometimes adjust mud properties prior to wireline logging operations to minimize risk of differential sticking.