My guess is that it was loaded as a 9mm, and you simply had an out of battery.
This is why I only buy reloads from companies who case gauge every round. I only know of one company in Canada that does this as it's very labor intensive, but it does guarantee that every round will properly chamber and that every primer is not upside down. Also nice to know that they powder check each case to prevent squibs and double charges..
Just my 2 cents
When you loaded your magazine didn't you notice the length difference. Either way it could have been worst.