Is a spell suppressed or removed when the target temporarily becomes invalid? [duplicate]

Question

Based on Jeremy Crawford's tweet, if a target is under the effect of an ongoing spell, and then the target changes such that it is no longer a valid target, the spell no longer effects them.

But does the spell end, or is it merely suppressed?

For example, suppose a human has been charmed by a dominate person spell. A friendly wizard casts polymorph on them; they fail their save and get turned into a sheep. This makes their type change to Beast, which is an invalid target for the dominate person spell, and the charm effect ends. The next turn, the wizard chooses not to concentrate, so polymorph ends and the target pops back into human form.

Assuming the dominating caster has maintained their concentration (if possible), did the spell simply end when the target became invalid, or does being invalid just suppress the dominate spell, which reasserts itself once the target is once more valid, like it would in an antimagic field?

Answer 1

The Spell Is (Probably) Suppressed

According to Jeremy Crawford (bold added):

There's no rule governing what happens when a valid spell target temporarily becomes an invalid target. A good rule of thumb is that the spell is suppressed while the target is invalid.

Although this is a "rule of thumb," and thus may not apply to all circumstances, most spells would be suppressed while their target became temporarily invalid, and would reassert themselves (if still ongoing) when the target became valid once more.

Answer 2

Spells continue unless otherwise stated

Most spells state target restrictions as part of the start of the spell, as is the case in Dominate Person:

You attempt to beguile a humanoid that you can see within range.

There is no additional text saying that the target must remain humanoid throughout the entire spell.

Likewise, there is no text anywhere in the rules stating that targeting restrictions follow some special set of rules.

The rules only do what they say they do

Nothing in Dominate Person says the target must remain a humanoid. Nothing in the Spellcasting rules states that targets must continue to be valid targets throughout the spell duration. There are no secret rules in 5e.

If you decide to play that spell targets need to remain valid targets for casting, there may be unexpected consequences

Summoned creatures will have to remain in line of sight of the player, some creation spells may pop out of existence after cast, some magical effects may cancel themselves out, there may be a host of new counterspell possibilities, there are a lot of problems that will arise from this ruling. Be aware that as the DM you will have to resolve these problems.