Why I can't transfer a Spinda using Pokemon HOME into BDSP?

I know that Spinda is obtainable in Pokemon BD/SP via a mass outbreak in Route 227 after obtaining the National Dex. However, Pokemon HOME won’t allow me to deposit a Spinda from BD/SP into HOME, and Pokemon HOME also won’t allow me to transfer a Spinda that I have transferred from Pokemon Bank (Spinda originating from Gen 7 or earlier) into BD/SP.

Why does this happen? Is there anything to do with the Pokemon’s compatibility or something, even though all 493 Pokemon from Gens 1-4 are coded into BD/SP?

P.S.: Spinda is not available in LGP/E, Sw/Sh, PLA, and S/V

Pleaselog inorregisterto add a comment.

Pokémon HOME cannot transfer Spinda into or out of Pokémon GO or Pokémon Brilliant Diamond and Shining Pearl, because of inconsistencies in how its spot pattern works.

In Pokémon GO, Spinda has nine predetermined forms rather than random patterns.

In Pokémon Brilliant Diamond and Shining Pearl, this is due to a bug in the game, which causes the encryption constant to be read as a big-endian value (i.e. bytes are read in reverse order), and would allow the possibility to indirectly change Spinda’s spot pattern. Spinda is the only Pokémon that cannot be transferred out of these games.

Spinda (Bulbapedia)