Quick hotfix. Sorry.

Updated to work for build 133 (Epic Missions Update).
As a fancy new addition, upgrading Epic items is now possible and properly costs Ore. These are obviously much more expensive than regular upgrades.

Map missions do NOT automatically upgrade gear. To compensate, the eligibility of an item upgrading after a boss kill only takes the base item level into account. Epic items can go up to +20, while regular items are capped at +15.

Another attempt to fix the multiplayer issue...

Moved the item upgrade code around. Hopefully it should now repeat for each player currently in the lobby.. Nope, still broken.
Thank you Thalios for pointing it out, and sorry for the inconvenience.