I think that Category tag of UFUNCTION is partial bugged in 4.5 release.
Code documentation said:
/// Specifies the category of the function when displayed in blueprint editing tools.
/// Usage: Category=CategoryName or Category="MajorCategory,SubCategory"
Category,
Greetings from the future. I just stumbled upon this as the first Google hit for “unreal engine blueprint function subcategory”. So let me provide a small update to this topic.
The | character for “MajorCategory|SubCategory” is still working as of UE 4.26.1 and nesting is allowed. The provided documentation link is dead and moved here.
Stating: