That's the terrible something I'm talking about. When using my Dillon 550B press, I make it a point to stop, clear all positions, and start over if anything disrupts my loading cadence.
Disruptions, lately, have been pieces of Blazer 45 ACP brass with small primer pockets -- they get a "What the heck?" when trying to seat a primer and loading stops.
I pull the troublesome case, take a look at the base, and see that a small primer pocket is the problem. The temptation is to simply toss that case, put another case in position one, and cycle the handle to de-cap and prime the replacement case. If I did that, there would be a double-charged case in position two.
I don't know about others but I adjust my chair height and position myself slightly to the left of the 550B so that I can see just a crescent of powder in position three where bullets are seated. No crescent means a squib load; more than a crescent means too much powder.