Archviles only do 20 damage in certain wads

[Ebenezer Menkinpare]

Problem persists in all maps of the WAD, even on these which don't have any archviles initially.
Some examples of this happening include 32innail (by Eternal) and DBP28 /idgames final build.
I run GzDoom 4.5.0 with no mods at all.

[Gez]

That means they don't inflict blast damage. Both these 32innail and DBP28 have DEHACKED that mess with the arch-vile's attack frames. Unless they do inflict blast damage in Crispy Doom and PrBoom+, I would not consider this a bug but a deliberate change made by the mod.

[Ebenezer Menkinpare]

That's the thing. They DO full damage in PrBoom+, that's an unintentional side effect. Didn't check it in Crispy yet though.

[Graf Zahl]

I checked DBP28, in this mod the fire is already gone when A_VileAttack is called. Apparently its animation got shortened a bit to free up a few states for other things or something like that. But it's the fire that is the origin of the explosive attack. It looks like vanilla accesses the stale pointer and is lucky enough most of the time that nothing bad happens.

The big issue here is that there is no good way to fix it. This is a classic case of undefined behavior - we simply cannot know if 'tracer' is null because no fire was ever spawned (in which case there must be no explosive damage) or because it had expired and the stale pointer had been collected by the GC already.
And even if it still contains a stale pointer we still do not know if it's from the fire or from some earlier residual data.