I've found an odd one.
I wanted to craft hotloaded medium ammo. I switched the craft window to Unavailable items.
Then I thought I might see if I could upgrade my armour. I clicked the little up arrow/chevron on the armour to see what components I'd need to buy... and the upgrade window was blank.
I tested it. I went back into the crafting screen and switched it to Available items and then went back to my armour... and then I was able to see the available upgrades to my armour.