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I have found a few of these "matte" reverse nickels in mint rolls. The field of the reverse side of the coins have a "matte" appearance and it is consistent in all of the coins I have found so far. Any thoughts as to what caused this effect?

Is there any chance that they are not actually rolls directly from the mint?
They look like they may have had an acid or base added to them to degrade the surface.

I know the mint set up a new Mint Shield product for coins, but last year there were regulation changes for surface coatings - I don't know if any of this actually meant changes for the mint's new coating out in 2018. And it is possible the new coating isn't holding up as well as they had hoped too.

I initially found 8 of them scattered in different rolls of an unopened mint box. I have found another 5 since then coin roll hunting various circulated boxes.
All of them are identical with the field being a bit "shinier" (almost unaffected) in the middle of the coin. There is a similar effect on some of the letters/numbers and leaves but not on the beaver.
I was wondering if it could be possible for there to be some kind of residue on the outer portion of the reverse die which produced a few of these coins until it wore off?

At a smaller scale this effect looks very similar to the coins in my posting titled "2021 What is causing this feature?". Especially the 2022 dimes.

Interesting comments on the surface coatings.

I reviewed all of the "Matte" Reverse coins I have found so far and found one that shows the "matte" effect starting to wear off/getting weaker.
For all of the photos below:
Left coin is the stage 1 matte effect coin
Right coin is the stage 2 matte effect coin ("matte" effect starting to wear off/getting weaker)

Still not sure what could cause this effect but I'm fairly certain it happened during the minting process.

Sorry,
Can't answer your questions.
But, i notice that on your nickels pictures some were missing some dots. Does it do or change anything on the values?
I've been collecting coins for years, never paid attentions on how to, what to etc... now in my 50s want to learn.
Thks for your attention,
Hope you get an answer on what you asked for.

Welcome to the Discussion board Grenette!
The missing dots, which we call beads, do not affect the value either way.