Crossbows not loading?

Sorry if there is an obvious answer but I've searched everywhere and haven't found a fix.

I have the moderate bolt quiver in my back slot, filled with iron bolts, and an empty off hand. I meet the stat requirements for the bows(both iron and diamond strengthened crossbows) and the bolts and crossbow are from the same mod(spartan weaponry). But I can't load the crossbow. It does the loading animation but when it ends it just goes back to the unloaded state.

Am I stupid?