When a firework is shot up from beneath a target block, most of the time it will activate the target block. However, if the firework was not placed directly under the target block, but still makes impact with the target block, then the target block will not send off a redstone signal.
Code analysis
See MC-178723.
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Hi there!
I can confirm.

This probably happens because it is calculated based on the center of the hitbox of the firework, simelar to MC-1133.
Can confirm in 20w48a.
Can confirm in 20w51a.
Can confirm in 21w03a.
Can confirm in 21w05b.
Can confirm in 21w06a.
Can confirm in 21w07a.

Can confirm in 1.17.1. Only happens when the projectile collides with the corner of the target block.