I maintain a number of snaps and regularly receive messages about packages that have been updated in the Ubuntu Archive, typically because of a USN.
For the past week or so these messages have referred to store revisions that have been superseded.
Taking the simplest example (which only has an edge revision):
confined-shell contains outdated Ubuntu packages
Revision r108 (amd64; channels: edge)
- libgdk-pixbuf2.0-0: 5554-1
- libgdk-pixbuf2.0-bin: 5554-1
- libgdk-pixbuf2.0-common: 5554-1
Revision r109 (arm64; channels: edge)
- libgdk-pixbuf2.0-0: 5554-1
- libgdk-pixbuf2.0-bin: 5554-1
- libgdk-pixbuf2.0-common: 5554-1
Revision r110 (armhf; channels: edge)
- libgdk-pixbuf2.0-0: 5554-1
- libgdk-pixbuf2.0-bin: 5554-1
- libgdk-pixbuf2.0-common: 5554-1
Looking on the “release & revision history” management page, I see:
latest/edge 155-mir2.8.0-snap77: 05 Aug 22 117: 155-mir2.8.0-snap77 118: 155-mir2.8.0-snap77 119: 155-mir2.8.0-snap77
And, for example, that “Revision r108” was superseded on 20 July.
It would appear that the notification messages are being generated from outdated information about the snaps.