Leaving any dashboards open in either IE or Chrome (No others to test) with a line chart (At least I think this is the cause) will eventually crash the browser or cause a memory error. If you look at Task Manager you can actually see memory use increasing over time.
This was reported back in December 2014 and a fix ensued.
Seems like we have the problem again. Some of my dashboards will require displaying on large screens 24/7 so this kills any planned projects with Ubidots.