I’ve seen a similar issue a while back, and I don’t think it ever got fixed, where Warhawk gets denied an extra turn if his initial damage kills a target with Hunter’s Mark. Heres a bug report from 2018 (there are many support threads dated earlier, going back into 2017):
I don’t think the issue was ever resolved, but I don’t have time to check right now. Maybe someone can do a quick check to see if this is around, because it is almost certainly related. Warhawk is definitely still bugged, does not give an extra turn casting on marked enemies if his initial damage is lethal.
The core issue is the same in both - status effect condition checks always fail if the target dies before the check is made. This is either due to all statuses having been cleared by the death itself before the condition check is made or because the target is now “dead”, and targeting is lost.
A tangentially related issue was with Orc Veteran, where skill point compares would also fail past lethality. This was reported (Orc Veteran not creating red gems if enemy dies [fixed] - one of many) and was apparently fixed in 3.2.5 per thread responses (confirmed it is working correctly now). A similar consideration needs to be applied to status effects condition checks as was done to skill point condition checks for the effected troops (either the check and therefore secondary effect is done earlier in the spell order or the relevant data needs to somehow be “kept around” for condition checks like this).
And yes, the Warhawk issue was an accepted bug report a long time ago and was apparently on their internal issues list (per my first linked thread responses, not sure why it ever got dropped off since it is still unresolved) and this is the same cause, so this is a bug.