I had that happen with Fiocchi Ammo a month or so ago with a new GP. The first day out Mine fired PMC and Blazer with no trouble, but couldn't close the cylinder with the Fiocchi's.(the last box of ammo I had at the time).
I thought it might have been crud buildup, took the gun home cleaned it up and still had that same problem. It had to be that batch of ammo as I haven't had the problem with anything else I've been shooting. The cartridges I was having trouble with just looked like they weren't sitting in the cylinder right.
I will say, these Ruger's have tight tolerances and it seems like you have to be careful when switching between .38 and .357. You can definitely feel the .357's hanging up after you shoot some .38's and have to be sure you get them in all the way. Might be better to just stick with the .357 loads until it gets a bit worn in.
But I also think they may be pushing out ammo so fast quality control might be slipping.
I'd rather have a gun and not need it, than need one and not have it!