I have not been able to find a wild Hisuian Sneasel or Sneasler with an HA to fully back this, though given the nature of the bug, it might not even be possible. While testing out the new Hisuain Pokemon that were added in 8.4.3, I found out that Hisuian Sneasel and Sneasler's Hidden Abilities (HA's) are not programmed quite right. In the PokeEditor tool, when you try to change their ability to their HA (poison touch), rather than just saying "Poison Touch", it reads "ability.Poison Touch.name". If you toggle this ability with the editor, the Pokemon will still get the ability and display it correctly in its summary. However, if you leave the ability on the Pokemon, log out, and log back in, on the first login, it will crash and say "Shutting down internal server" briefly, then it will display a message saying "Connection Lost - A fatal error has occurred, this connection is terminated". If you try to log in a second time, it will boot with no problem. However, the Sneasel/Sneasler ability will be set back to its default ability. I was told by a friend that this is a similar bug that occurred to Indeedee with its HA when it was introduced, though I am not certain if it is exactly the same. This was all tested in a private, local, single-player world so I am unsure how it may behave in a public server setting, though I imagine it would have similar results. I am aware that 8.x.x is receiving very limited support now as your focus has shifted towards 9.x.x, but for the few of us that have to hold out on 8.x.x for certain reasons, we greatly appreciate this surprise update, and would really appreciate it if this bug could be fixed in a small update. Thank you for your time, and have a good day!

Hi there, I've had a look into this issue and I was able to reproduce the login failure you mentioned, and eventual loss of the ability upon getting into the world. While the team has decided further updates for 1.12.2 are unlikely, it turns out this issue can actually be resolved via external json files.

The problem is that the stat files attempt to give the ability "Poison Touch", whereas the ability is registered as "PoisonTouch" (consistent with all the other multi-word abilities). This can be seen in the lang key which appears in the pokemon editor, containing a space where one should not exist. Upon world reload, such an ability cannot be found which causes the bug to occur.

After enabling external stat jsons from your pixelmon.hocon, the files for Sneasler and Hisuian Sneasel can be updated accordingly - changing the ability "Poison Touch" to "PoisonTouch".

Unfortunately this is unlikely to see an official fix, but at least it is possible to resolve this with external files - hopefully this helps!