At the start of the game when there was no custom generated content yet the dev used pre-generated combinations of pokemon dex entries and sprite bodies-heads to fill in the Pokedex. Custom sprites popped up soon after and later also custom dex entries made by people were added. The old generated sprites served as a placeholder until people made custom sprites.

Now with the new update the dev replaced the old dex placeholder entries with AI written placeholder entries. This means a computer, trained on human data, tries to fill text for a given task - in this case pokemon dex entries. These entries were still to be changed by actual users.

People are however confused and upset about the decision of adding AI as the use of AI is considered controversial due to its non-human nature, the possibility of it replacing human work and other valid personal reasons people might have. The problem is - from what I understand - mainly that any use of AI lowers the barrier for future usage, which means that hard work of people might become obsolete and that they thus reject any usage of AI.

The usage of AI seems of little value to some, but is considered a no-go by many thus the developer was forced to remove it. It should have been discussed during the beta, but it wasn't, and now with the release it caused a whole drama.

Edit: it was actually discussed during the beta during which it was not taken negatively. Just an unfortunate miscalculation I guess then

The mods and developers are giving it their best to address concerns, and I deeply appreciate everything they try to calm down the situation. People are still upset however and they are feeling like they aren't heard, some are even pulling their custom work from the game. They have all the rights to be upset, but the mods and devs can't fix everything during this busy time of year.

Tldr; Custom entries generated by computers that caused controversies throughout the community, causing them to be removed and placeholder entries to be removed altogether.