I just got a couple of Rpi 3 B+ and they work really great with the latest Rpi Image 2018-03-13-raspbian-stretch.img. However, I wanted to install ubuntu 16.04.2 or ubuntu-mate-16.04.2, but neither will boot. The red LED turns on and stays on, or in the case of ubuntu-mate it blinks slow 4 times, then fast 4 times, then the same cycle again. I tried these img files with the previous Rpi 3 B and they run fine.
Is there an ubuntu image I can find that will work with the new B+, or is it a known issue?
I didn't find the right solution from the Internet.