I’ve discussed this with the development team and they have confirmed that a Valraven can replace a Doom Troop during a Tower of Doon event. When this happens that it is counted as a defeated Doom for the player, so you’ll still get the Scroll as well as the Sigils for defeating the Battlecrasher.
Thank you for pointing out the UI issue with the Collect button in the Tower of Doom rewards screen. I have reported that issue to the development team to get fixed.
OminousGMan - Support Human