Unable to receive Mystery Gifts (Pokémon Black/White 1 and 2)

Hi!

Yesterday, I started a new game of Pokémon Black Version 2. After I progressed a bit in the game, I wanted to receive the Mystery Gifts of the game with the Poké Classic Network. However, after receiving some of them, I get an error message saying that no Mystery Gifts are available. After doing several manipulations to try to solve this problem (in vain), I noticed:

that the connection between my 3DS and the Poké Classic Network works
that only the Mystery Gifts don't work for me (the GTS works)
that I have this problem on ALL my fifth generation games, and it doesn't happen on my fourth generation games

I know since today that I am not the only one with this problem, because someone on Discord also mentioned it.

mm201 / pkmn-classic-framework

Unable to receive Mystery Gifts (Pokémon Black/White 1 and 2) #103