I have heard someone complain that his Lee dies kept working loose. Lee uses an O-ring in the locking ring that forms a friction lock. When I turn a Lee lock ring down tight, I have never had a die work loose and can't imagine how it works loose. I tried to ask if his lock rings have an O-ring and he said he didn't care--they worked loose and he now had the dies "duct taped" down so they wouldn't move. I wonder if some people just don't understand lock-rings or what?
With any progressive press, go slow, read the manual and reference at each step, check everything in the beginning, be prepared to call the manufacturer while you are at the press if you have a problem, don't force anything (remove all cases from the shell plate and determine the cause of the problem), and KEEP THINGS CLEAN. If you spill some powder, stop, remove all case, remove shell plate, and clean up the spill. If the powder works its way over to the priming system, it can really mess things up.