Pokémon Sleep version 3.8.0 has resolved several in-game bugs affecting sleep research, missions, sleep tracking, Pokémon GO Plus + and smartwatch pairing, as well as Munchlax’s Nap Island. One sleep research issue could trigger Error Code 001001 and return players to the title screen under certain conditions, while display errors could affect the Missions screen’s days-left counter and sleep tracking duration. Another bug on Munchlax’s Nap Island could prevent the game from progressing when taking Pokémon back after they reached Lv. 70, although restarting the app provided a workaround before the fix. Pokémon Sleep confirmed that none of these issues affected game progression and that all listed problems have been resolved with version 3.8.0.
Source: Official Pokémon Sleep news
Nintendo & Pokémon Blog 