With me, it was probably a combination of bad/not enough lube and the weak, IMO, rim on the 5.56 cases, and finally the loose Lee shell holder. I have since switched to RCBS shell holders, which are tighter and hold the rim better, and to Imperial Lube, which so far has been great, no stuck cases. Now, I have stuck a couple cases before, but with the Lee dies, all I had to do is take the die apart and tap the case out. With the RCBS dies I couldn't do that without possible destroying the decapping pin or rod. No issue replacing it, but I had 2k cases to convert, 1k 300BLK, 1k 277WLV, so couldn't wait. The Lyman was available over the counter at my LGS, had to call around, but it unstack all 4 of the ones that managed to get stuck, out of the 2k.
So, just got this thing in the mail, and I must say, it should be much better than the one I have, or any other methods mentioned so far. It has jaws that should hold the rim very tight, and the stud part floats along a channel to snap it into the ram. Which means no disassembly, no damaging anything...unless I pull the case in half