There is a known repeater problem with many types of zigbee bulbs connected directly to the smartthings hub, whether they were originally ZLL or were only ZHA. ( The problem does not occur with bulbs connected to the hue bridge, because those bulbs will not try to repeat for your other zigbee devices. )
The bulbs will typically repeat fine for other bulbs.
Anyway, when traffic is high, the bulbs can get a kind of “buffer overflow” condition where they will simply drop messages sent to them to repeat.
Smartthings engineers have been testing this issue for over a year, but it just keeps cropping up with multiple different brands of bulbs.
See the community FAQ, which includes links to staff engineer comments.
