rod side clearance.

And this is one easy place to make a mistake. You were measuring between the rods right? This is, or can be, very tricky; since the feeler, if too fat likes to spread the rods.Then it fits at the top, but jams when approaching the crank.
If you are measuring after the short block is assembled and the engine is upside down on the engine-stand, then this is less of a problem. Certain rods have to be installed in certain directions.
But you probably know all that.