Invalid Apple Watch icon file names must match pattern "*<dimension>@<scale>x.png"

For me, the issue was that I still shipped the watchOS 1 Long Look icon (44X44@2x) even tho I no longer supported watchOS 1. Once I unchecked the bod for watchOS 1.0 in the assets and deleted the no longer needed icon, I had no problems.

I had the same problem, none of the sollutions above worked for me.

Instead of submitting the app, I exported an IPA, and had a look of its contents. Turned out there was duplicates of my icons in there, but named differently.

I renamed my files according to the files I found, drag and dropped them to their places in AppIcon, archived, submitted and IT WORKED!

Proper naming of the WatchKit icons:
AppIcon24x24@2x.png
AppIcon27.5x27.5@2x.png
AppIcon29x29@2x.png
AppIcon29x29@3x.png
AppIcon40x40@2x.png
AppIcon44x44@2x.png
AppIcon86x86@2x.png
AppIcon98x98@2x.png

I got the same issue when I tried to submit. My problem was that I was sharing my image asset file with both my iOS app target and my WatchKit app target. You need to have a separate image asset file for your WatchKit app and it should ONLY have images for the Apple Watch in it. That fixed it for me.