Hello 3Dnerd,
I am indeed using white PLA, the roll is about 5-6 months old, and was stored in an airtight container with a moisture eater. I would raise the temperature, but the strange thing is that the bottom layers are absolutely fine but it is only the top that appears to have this issue, almost as if something has changed halfway through the print. I will retry tomorrow with a higher temp.
as far as I can tell there is no major difference in technology or mechanics between the UM1 and 2, but I may be wrong on this as I have only seen the UM2 in videos so far.