Please post a photo.

Hope your garden is large for your Mahonia I keep mine to just 6ft and away to cut top off to take back to 5ft.

The new leaves lower down on my mahonia are brown as they appear. When the berries on the mahonia have been eaten eagerly by starlings and the blackbird I will take back the taller growths back to let more light to other plants,as the sun comes over it. It would take a lot to clobber a well established mahonia.