In a Duskmourn Sealed game last night, my opponent attacked with 6 creatures, including one flyer. I clicked with my creatures to block all 5 of the non-flying creatures. To make sure I wouldn't take lethal damage, I did a double-check, hovering over each attacker to make sure I was blocking them as intended.

Somehow, I took damage from one of the non-flying attackers, which was lethal. I would have won the following turn. I have no idea what went wrong in blocker selection. It did not have trample. I believe a blocker got unselected somehow, either through a misclick or a bug. But because of how carefully I was taking my actions and double-checking them, I don't think I set them up incorrectly.

But honestly, the blocking UX is kind of confusing, because there is not much visual contrast between a blocked and unblocked attacker. This is not much of an issue with simple combats, but it quickly becomes visually overwhelming with all of the colored arrows in a complex combat with >10 total creatures.