Hi Juraj!
So once you are facing this issue, there is no way to fix it unless you do a rollback?
We are currently facing something pretty similar... we updated the Hotfix from 13.0.135 to 13.0.178 and after that, everytime we head to Categories and create a new one, the Form Control is not rendering correctly into "Allowed page types" tab.
I think it should be a programmatic way to fix, don't you think?
Following is a brief segment of our Event detail:
Description:Message: Form control '' not found.
Exception type: System.InvalidOperationException
Stack trace:
at CMS.FormEngine.Web.UI.EditingFormControl.CreateControl(FormFieldInfo ffi)
Event URL:/Admin/CMSModules/Categories/Pages/Administration/Category_List.aspx?siteId=
URL referrer:https://mxl690-pf40ve0x.ipgphotonics.com/Admin/CMSModules/Categories/Pages/Administration/Category_List.aspx?siteId=