What caused my grass-fed beef to taste & smell ‘off’ this time? Not sure if gamey or barnyard-y is the right description
Based on your explanation I can only speculate a bit. I have ordered beef and other meats including yak (which is from a bovine) online from various places.  I prefer grass fed and free range beef and also eat some game meats (venison, rabbit, ostrich, boar, etc) so am familiar with some variety of meats besides the farm raised packaged meat in most grocery stores.

Free range meat tends to be leaner, and a bit tougher and gamier, with stronger smell and flavor, than grocery store meat. The best way I'd describe "gamey" is a flavor somewhat like liver, and sometimes what seems like a slightly powdery texture or mouth feel. It can indeed smell a bit musky. The meat tends to be leaner and tougher and so depending on how you prepare it can be chewier. Not sure if this describes your experience? One person might find this appetizing while another might find it off-putting.

In my experience the fat on free-range meat often has a yellow color rather than pale white, has a stronger smell and flavor, and often a lot of the gaminess in the meat is actually in the fat. So if it is very well trimmed you can eliminate some of that.

Another possibility is that the meat wasn't handled well between slaughter and when you got it. The meat needs to be hung before it is processed, as short as 3-5 days and as long as 21, this varies based on the animal and how it is prepared, and this is where the experience and quality of your producer come into play. It is not true that fresher i.e. closer to the slaughter date is always better, the meat needs to hang for a while to become tender. A cattle is a huge animal, hundreds of pounds, and it takes a while for the meat to age before processing. It could also be that something went wrong with the shipping, maybe the steaks were allowed to thaw and refreeze or exposed to air.

I would take all of these questions to your beef producer and see if you can figure it out.