I am having a similar issue with my UM2+ running with the firmware that came with Cura 15.04.4 (will be updating to 15.04.5 once the print finishes). Did you ever figure out a fix for this issue? Backstory: I am running a 28-hour print (scaled up version of the included tetra-wire example model), the screen seems to have locked up around 13 hours left with a line through the top line of text (and part of the second line) like a strike-through. There is no response to the control wheel, either rotating or pressing. The print itself however is still chugging along, I just can't tweek any of the print settings on-the-fly now with the UI unresponsive.