PH2: Level-Exp Bug, Pokémon GO Transfers .

Observation of the Level-Exp Bug

Around June 15th 2023, 10am (UTC), it was noticed by players on mobile, certain Pokémon being sent from GO to HOME has the Level of 1 with a Level 100 moveset.


It was subsequently discovered that in HOME on the Switch, they appeared to be Level 100.

It was also discovered that if you were to transfer such a Pokémon to Scarlet & Violet, viewing the Summary Screen would cause the game to crash.

It was around June 15th 2023, 3pm (UTC), that players noticed that this issue (level-exp bug), as well as issue where XXS from Pokémon GO becomes random height (XXS-Height randomization issue), were both fixed.
 

How the Level-Exp Bug works

According to a message left on Discord by Matt (@sora10pls)(Mattyoukhana), depending on a species' experience growth rate, HOME applies an incorrect experience value to the Pokémon upon transfer, with only the Medium Fast experience group being affected.

An example to look at would be Mythical or Legendary Pokémon. They are in the Slow experience group, and they got 0xFFFFFFFF written to their experience. As such, they appeared to be Level 1 or 100, due to how the device deals with the value of experience.  (Pokémon data don't have Current Level as a data point in the data structure; it is instead derived by the experience stored in it)

As such, it is dubbed the GO->HOME Level-Exp bug.

 

A 'fix' on the user end

As described by Matt, move the affected Pokémon into a compatible game, do not view the summary, and send it into a battle.
The experience it should have would then be fixed by the game, and it will become a regular Level 100.

Conclusion

The prevailing theory is that when attempting to fix the XXS becoming random height issue, Pokémon HOME borked the code for handling experience values to match the GO Trainer's level, thus creating this secondary issue. It is currently unknown if HOME will revert or fix the levels of Pokémon that were already transferred. (Pokémon that were sent into HOME during the buggy period currently continue to have bugged levels in HOME)

Additional info: Background for the XXS-Height randomization issue

With the launch of HOME v3.0.0, Pokémon from previous games could be transferred to Scarlet & Violet. In Scarlet & Violet, if the size of a Pokémon is the smallest or the largest (in terms of scale), it qualifies for a Mini Mark or a Jumbo Mark respectively. Thus, players would want to transfer the XXS or XXL Pokémon from Pokémon GO and obtain these marks.

In the initial weeks of HOME v3.0.0 launch, players have noticed that their XXS Pokémon from Pokémon GO were average sized when transferred to Scarlet & Violet, thus being unable to qualify for the Mini Mark. As it turns out, Pokémon HOME has been rerolling the Height and Weight values of any Pokémon that had 0 in both stats (explained in Route B on this page), and XXS Pokémon from Pokémon GO were caught in the crossfire.

Files and contributors

The files uploaded here are contributed by @theSLAYER and @sora10pls.
They have been dumped in HOME format (PH2) and converted to PKX via PKHeX for usage with the games.
The OT, TID, and SID has been changed for privacy purposes.

As these files stand, they'll be similar to a player transferring a Pokémon from GO and leveling it up to 100.
In some sense, the only 'special' copies would be the originals (those that have the GO stamp), with the bugged levels, in Pokémon HOME.

It is also important to note that the bugged originals in HOME cannot be traded via HOME.