Can't edit build items in categories

[apocthelegend]

I click edit build, I click on a category, I click to add an item to it or remove one, nothing happens.

Video attached.

 

[bambini!]

The most frustrating part is that sometimes edit works properly but breaks after some time for no reason

 

[Gooball]

I was a dummy. You have to have the category in your build selected first.

 

[Guilty]

I have the same problem