I tried a few 0 % missions, this is what I've learned so far:
If it's a mission that requires more than one follower, the UI glitch won't happen and therefore I can't open the chest.
If it however only requires one follower (which shitty missions do) you can use this bug to open chests. I have only been able to test two 0 % missions with either gold or GR, and I happen to get both, so I can confirm that it was working for me. Keep in mind that it did NOT work when it required two-three followers. Then it would simply just quit the mission window and the chest would be gone.
So... at least (for me) it only works on mission with one follower, which only makes it usable on new characters with shitty followers. Don't expect to get highmaul gear with this.