You can use in-game matchmaking to snag infinite crafting materials, at least until such a time as the developers fix a glitch that makes that possible. When you first log into the game, find materials you'd like to farm and collect them. Then pause the game and enter the Group Management tab. Select Matchmaking, then Automatch, and finally the Free Roam option.
When you join another session, the materials you collected should appear again, so you can collect them once more. You can repeat the process as often as you like with any material that is available in respawning crates, making it easy to craft excellent weapons and armor.