I believe Geta categories is intended to replace the inbuilt categories in Episerver so the property disappears because the Geta categories library hides it here:
In terms of a solution, you could build your own modified version without the file referenced above and use that in place of the nuget version. You could also raise an issue on github to make hiding the category property optional. Your existing solution would probably be inconsistent as it will depend on the order in which things run. If your code runs after the Geta code, the field will show otherwise it won't.
Yes Paul is right, we use it and it's a total replacement for the Category system.
After upgrading Episerver CMS from 10.x to 11.11.0 and installing geta categories the Episerver Category property has disappeared from all pages blocks. I have checked the code and upgrade changes but there is no way in the code the category is getting hidden. The only way to bring the Category property back is by using the following code http://joelabrahamsson.com/hiding-episervers-standard-category-property/ and setting metadata.ShowForEdit = true;. This an ugly solution and some editors complain that they are unable to see the category property sometimes and sometimes it just appears as normal.
Any ideas about why the property disappear in the first place? any solution?