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Unreleased music, probably Movie 7's unused BGM. It's also possible that it's the beginning part of our version of the track
Movie 7 BGM - Underground Hideout (that played right after the one below), where only the part recorded in the site's database was heard in the movie, but the previous part existed and remained unused by the anime producers in the full-length feature. Still, it's just a theory and the track should be marked as a regular unreleased BGM.
There's a similar case with an unused music from Movie 2 (I'm absolutely sure it's from Movie 2, but wasn't used in the movie itself), but I won't bring it up seriously until at least the end of DP.
I hope I made myself clear.
AG 172 - 05:47 (Hinata explains to the group that last week strange things began to happen around the Pokémon Center.)