Incorrect Screen Time calculation on iPhone 15 Pro Max

In your case Refer to Pic 3 below, there are three Categories*** displayed Social "1" (Blue), Utilities "9" (Aqua), and Health & Fitness "8" (Orange).

Every other Category*** is shown as Grey. i.e. 2,3,4,5,6,7,10,11, and 12

Refer to the list of Categories listed below and pic 1 where Category Serial No. 1 (Social), 7 (Reading), and 12 (Others) are shown Blue, Aqua, and Orange

In this case (Pic 1), all other categories serial nos. 2,3,4,5,6,8,9,10 and 11 are Grey

Pic 1

Look at the pic 2 below a cut-out view of a screen from an earlier old post

Pic 2

Total Screen Time is a+b+c

*** There are 12 board level Categories in Screen Time

1. Social Networking: FaceBook, Hangout, Instagram
2. Games: Scrabble, PUBG, Sudoku
3. Entertainment: TV, Music, YouTube, Netflix
4. Creativity: Photos, Camera, Google Photos
5. Productivity: Shortcuts, Mailk
6. Education: SkyView, Learn Python
7. Information & Reading: Wikipedia, Magzter, Weather, Kindle, NDTV
8. Health & Fitness: Journal, Tata 1mg, HeartRate Pro, Activity
9. Utilities: App Store, Measure, Truecaller, Calculator
10. Shopping and Food: Amazon, BigBasket, Shell Asia
11. Travel: Apple Maps, Google Maps, FlightAware, Booking.com, Uber
12. Others: Pinterest, iTunes Store, Kia Connect

The graph displays the top 3 (Time used by the user) category legends on the X-axis. Anything other than these legend categories is a Grey bar in the graph

Pic 3

For example:

If the user has used Games, Entertainment & Others category apps for the maximum time during a period then the graph will show these three categories in the X axis as legends and the remaining categories will be shown in Grey Colour.

The GIF below will illustrate the graph from 3 iOS devices

iPhone 6 iOS 12.4.5

iPhone SE iOS 13.3.1

iPad Pro 9.7" Wifi+Cellular iOS 13.3.1

GIF 1