The switch on the board gets a bit of center so the boots rubber nub doesn’t get good contact to the switch on the board, actually the rubber nub on the boot is really to soft and bends to much, so you have to take the retainer and boot off and get the switch centered and then it will work great, I did a picture write up during a group buy for the UT01 & 02, it was a buy put together by George, I think I’ve spelled his name wrong but it’s close,
Edit: By the way to take that retainer off if you don’t know, I take a small screw driver and carefully pull back from the sides of the boot to pull the boot edges out from under the retainer and then with the boot out I can take a bit bigger screw driver and gently pry up around the retainer to remove it being careful not to bend it, it’s soft alum, the retainer is just pressed in.
Then take your small screw driver and put it on the side of the switch box, it’s normally off center to the left of what would be centered but anyhow then gently just pry it over until it’s centered then put the boot on and then press in the retainer and your good to go.
I’ve had very few that I’ve had to do that more than once, great little lights or they were anyhow.