It could also be possible that NPC's were spawning the same frame others were dying and I used the boss summoning item, that's my most likely theory for the sequence break to clarify what I said below

It's a vanilla bug but normally isn't possible due to the much lower potential spawnrates with items. I think the reason the bug happened in my screenshot is because a certain number of NPC's were spawning at once that sequence broke the Ravager, the same is possible with the Destroyer and any other segmented boss (including Skeletron and Prime) but the base of the boss is still guaranteed to spawn even if there's only one slot left out of the 200 maximum.