Still happening as of 22 September 2024, I had 5 creatures but created 9 roles with Doppelgang. It wanted 9 different creatures, but of course I couldn’t select that.

It should be possible to multi-select the same creature even if there are enough creatures available. The game rules allow it, and the player chooses the role that remains.

Bumping this with another aura - Doppelgang for X=12 included targeting a Witness Protection, but with only 5 targets on the battlefield, the UI couldn't handle me selecting the same permanent multiple times to resolve it appropriately. Eventually, the timer ran down and stacked all 12 copies on the creature that was originally enchanted, very unhelpfully. Some sort of mechanism for selecting the same target multiple times when a large quantity of auras are entering simultaneously seems to be in order?

I had the same problem. Opponent cast coerced to kill on my Agrus Kos, Spirit Of Justice. I cast doppelgang targeting the coerced to kill and one of my riftburst hellion. It's almost like it wanted you to submit 2 but would only allow you to submit one but because I hadn't submitted to. I had to wait until the game timed out.

Still happening as of march 17

This happened to me as well with due diligence