Previously you were able to harm all Pokemon outside of battle, such as through the use of harming potions and swords etc.
In 8.1.0 it was changed so that Ghost types are immune to all damage except Magic damage, which led to the ghost drops issue.
This was resolved however now Ghost types cannot be killed through magic damage or even other physical methods. This is causing issues with mods such as Morph, which requires the mob to be killed by the player themselves. This occurs with dual-type Pokemon too

Moved to internal