yes, we are seeing this as well
the reactor intermittently is working fine and if you watch it tick for 20 minutes it fine, but you leave for a little while and come back and it is still ticking and consuming the cells but is generating no power...you pull cells and replace them again and it still generates no power.
I have yet to find a why to get it generating again, seems if I wait long enough to replace the cells it starts working again.
I have a chunk loading block under it and it still seems to stop, and I am pretty sure I have had it stop while I was looking at it once as well, so not sure what is going on with it