Shield spell - removing the special effects of a hit [duplicate]

Question

Background

A Shield spell is cast as a reaction to an attack that hits. It applies its AC bonus even against the attack to which it is a reaction, meaning that it can make the attack that hit, retroactively miss and thereby not do damage.

Shield 'interrupts'/potentially cancels its trigger, as stated in the DMG in the 'Adjudicating Reaction Timing' section.

Since the hit has retroactively become a miss, what happens to effects that were triggered by the hit in the first place? Are they undone as well, or do they persist?

Does blocking an attack with the Shield spell still trigger Armor of Agathys? has two answers of nearly equal popularity, with one arguing that other effects triggered by the hit still persist, and the other arguing that they do not. On the side of the argument that they do not occur is a (now-unofficial) tweet from Jeremy Crawford stating

If the attack has a special effect that relies on it hitting, that effect doesn't occur if the attack is turned into a miss.

However, the discussion on both sides therein focusses on a narrow interpretation of 'effects' as discrete, measurable things that happen to specified targets - the hit on the caster of the Armor, and the resulting damage to the creature making the attack.

Are the 'special effects' of an attack referred to limited to things like damage or conditions that affect just the target of the attack, or do they include intangibles like knowledge for all intelligent observers?

Scenario

A party is traversing wilderness with abundant natural cover as well as opponents who are seeking to ambush them.

A hidden opponent fires a missile weapon at a party spellcaster and hits. In response, the spellcaster uses the shield spell and turns the attack into a miss. However, the ambusher has now revealed their location to the spellcaster and everyone else in the party, since according to the rules of Unseen Attackers and Targets

If you are hidden--both unseen and unheard--when you make an attack, you give away your location when the attack hits or misses.

The party members begin to defend themselves and target the ambusher.

The next round, a second hidden ambusher also fires at the spellcaster, hits, and also reveals their presence to the caster and the rest of the party. The spellcaster again uses shield, and again converts the hit into a miss.

This second ambusher, however, possesses the Skulker Feat (PHB 170)

When you are hidden from a creature and miss it with a ranged weapon attack, making the attack doesn't reveal your position.

Since the attack was now actually a miss, does the knowledge of ambusher's location persist as revealed, or is this knowledge undone?

Does...
...the shield spell travel back in time, converting the hit to a miss before the party had knowledge of the second ambusher's location?

...knowledge of the ambusher's location count as a 'special effect' of the attack hitting, that now does not occur since the attack resolved as a miss?

...the 'special effect' of the knowledge of the ambusher's location get removed from only the caster, while their companions still know where the ambusher is?

...the knowledge of the ambusher's location not count as a 'special effect' of the attack, but rather as mundane effect, that is not changed by the shield spell?

A good answer may use the Crawford quote or not. If it does, it should convincingly interpret what is a 'special effect' and to whom it applies. If the answer does not use the Crawford tweet, it should explain from where it draws its reasoning.

Answer 1

Shield spell influences the consequence of attacks, both hit or missed.

Some attacks has consequences depending on having hit or miss: then, the Shield spell may trigger the condition to be met for both cases, and sometimes it could be quite difficult to decide if these conditions are met or not (see for example the Q&As [1], [2] linked in comments).

Nonetheless, the depicted "ambush scenario" has a clear solution.

The 2nd ambusher's position is not revealed.

The events are

1. The second ambusher attacks the caster and hit them
2. The caster uses their reaction to cast Shield and the attack results in a miss
3. Since the attack is a miss, the Skulker Feat allows the second ambusher to keep its position hidden.

The rule for Unseen Attackers and Targets as you reported says (emphasis mine)

If you are hidden--both unseen and unheard--when you make an attack, you give away your location when the attack hits or misses.

In the depicted case, the Shield spell has no role for the first ambusher: in any case (hit or miss), their position is revealed by the attack. The case for the second ambusher is different, indeed the Skulker feat is the specific rule that overcome the general one: when the attack miss, the position remains unrevealed. If the Shield spell causes the attack to miss, it triggers the condition for applying the Skulker feat. If the attacks hits, then the position is revealed.

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From a narrative point of view, the caster sees the arrow coming just in time to cast Shield and be protected, but they did not see the direction from which it was shot.

Answer 2

The Shield spell is effectively time travel.

If the caster's normal AC were e.g. 16, and they cast Shield in response to an attack, then the attack should be resolved as if they had always had an AC of 21.

There was never a point (in-game) where that attack hit. The attacker rolled their d20, came up short of the 21 that they needed to hit, and therefore missed.

As such, all of the situations you mention are handled the same as if the attacker just rolled poorly and missed the initial 16 AC; the second enemy is still hidden thanks to Skulker, since their attack missed the target.