Hi,
Yes I did those tests. The first was 5v. The second test was a little higher at about 3.8v. Though I have a crappy volt meter do it is a little hard to read.
Yes I have a 24vac supply 875mw. I tried it with a second power supply 24vac 700mW and the board behaved the same way.
I found that if I kick start the board with the USB I can then turn on the power and disconnect the USB and the 24v. Seems to maintain everything up and running.
Peter.