It doesn't matter how popular the powder, they do very.
While they do
vary, it's generally within a 3% range, not 10%.
The OP is using a low load in a powder that is intended as hot loads.
According to Hornady, the OP is loading a charge that falls dead center in the load range for a 125 gr jacketed bullet(generally a good range for plated bullets). I know that Hornady gives some anemic recipes for H110/W296 in .357, but they are not unsafe. Do you honestly think Hornady does not know about the risk of a stuck bullet with low powder charges of H110/W296? Do you honestly think they don't have the knowledge to allow for the slight variance in powder lots to keep their recommended start loads safe? Do loading manuals not tell us to start at the suggested start load and work up? I've yet to have one tell me to start at max and work my way down.
Has something changed? Sure it has. Could be bad powder, but could be bad primers too. Could be wrong primers. I only buy primers by the case after seeing store clerks picking up loose primers and stuffing them back into 100 count boxes after customers had to open and spill them. I often wonder how they know which are which.
Everyone recommends three things with H110/W296 in small cases like .357. Stick above recommended start loads, use a magnum primer and a firm roll crimp. Sounds like the OP did this....as far as he knows. The reason for the suggestion of all three, is that all help with ignition of the hard to ignite powder. The statement of a squib followed by a flamethrower type load makes me think of a difference of powder charge, difference of primer or difference in crimp. As I said, plated bullets are difficult to roll crimp. Too soft of a crimp and you don't hold the bullet firmly enough for good ignition ind to prevent jump and crimp them too hard and you deform the soft lead bullet under the plating and end up worse than little or no crimp. Jump crimp just a tad in a revolver and you increase case capacity and can greatly decrease pressure. Plated bullets, IMHO, are best with a taper crimp and low to moderate velocities/pressures, and thus best with faster, easy to ignite powders.
Yes, there are better powders for plated bullets at modest velocities. I certainly would not use the combo the OP is. But in truth we only know the OP thinks he has a correct powder charge(hasn't pulled any bullets), claims to have used magnum primers and used a proper crimp. Did he use mixed brass with different case tenths, wall thickness and mouth hardness? I dunno. I'd like to see what Hodgdon has to say about the lot number. All any of us can do is take a WAG as to what happened. Could be a combination of things, not just one. A slight mistake in powder charge and a light crimp or a light crimp combined with mismarked or bad primers. Could be a contamination problem with either primers or powder. As I asked before....was there any moisture used with cleaning the brass? I have seen case polish clump in brass and have seen folks who thought their washed brass was dry. Both critically affected the way the ammo performed. Would upping the charge decrease the risk of a squib? Of course it would, but it wouldn't prevent one of there are some of the other issues going on that have been mentioned here. You are correct.......
with a marginal load to start with it does not take much.
) and introduced it as W296, and later just 296. So Hodgdon actually has longer experience with it.