I’m on version 25.0, build 1161 on Android. My apologies if this bug is on the known list. I remember seeing something about blacked out heroes showing up on the battle screen but it never happened to me before this version of the game. It also happened during the middle of a war hit. This screen cap is the triggering event. I’ll link the video of the hit below.
This video starts a couple seconds before MoNo blacks out.