Run snap info on the downloaded snap, rather than against the store. First of all snap info doesn't have --channel argument, thus queries the wrong channel, and depening on the cohort, a different snap might be visible too. Thus seed the base of the snap revision we dowanloaded, rather than some random one from the store.

debian/changelog

@@ -1,3 +1,13 @@
+livecd-rootfs (2.663) UNRELEASED; urgency=medium
+
+  * Run snap info on the downloaded snap, rather than against the
+    store. First of all snap info doesn't have --channel argument, thus
+    queries the wrong channel, and depening on the cohort, a different
+    snap might be visible too. Thus seed the base of the snap revision we
+    dowanloaded, rather than some random one from the store.
+
+ -- Dimitri John Ledkov <xnox@ubuntu.com>  Fri, 17 Apr 2020 00:00:52 +0100
+
 livecd-rootfs (2.662) focal; urgency=medium
 
   * Print subiquity ssh login details on s390x line based consoles.

live-build/functions

@@ -482,6 +482,24 @@ _snap_preseed() {
         return
     fi
 
+    sh -c "
+        set -x;
+        cd \"$CHROOT_ROOT/var/lib/snapd/seed\";
+        SNAPPY_STORE_NO_CDN=1 snap download \
+            --cohort="${COHORT_KEY:-}" \
+            --channel=\"$CHANNEL\" \"$SNAP_NAME\"" || snap_download_failed=1
+    if [ $snap_download_failed = 1 ] ; then
+        echo "If the channel ($CHANNEL) includes '*/ubuntu-##.##' track per "
+        echo "Ubuntu policy (ex. stable/ubuntu-18.04) the publisher will need "
+        echo "to temporarily create the channel/track to allow fallback during"
+        echo "download (ex. stable/ubuntu-18.04 falls back to stable if the"
+        echo "prior had been created in the past)."
+        exit 1
+    fi
+
+    mv -v $seed_dir/*.assert $assertions_dir
+    mv -v $seed_dir/*.snap $snaps_dir
+
     # Pre-seed snap's base
     case $SNAP_NAME in
         snapd)
@@ -494,7 +512,8 @@ _snap_preseed() {
             # Determine which core snap is needed
             local snap_info
 
-            snap_info=$(snap info --verbose "${SNAP_NAME}")
+            # snap info doesn't have --channel, so must run agains the downloaded snap
+            snap_info=$(snap info --verbose ${snaps_dir}/${SNAP_NAME}_[0-9]*.snap)
 
             if [ $? -ne 0 ]; then
                 echo "Failed to retrieve base of $SNAP_NAME!"
@@ -510,24 +529,6 @@ _snap_preseed() {
             ;;
     esac
 
-    sh -c "
-        set -x;
-        cd \"$CHROOT_ROOT/var/lib/snapd/seed\";
-        SNAPPY_STORE_NO_CDN=1 snap download \
-            --cohort="${COHORT_KEY:-}" \
-            --channel=\"$CHANNEL\" \"$SNAP_NAME\"" || snap_download_failed=1
-    if [ $snap_download_failed = 1 ] ; then
-        echo "If the channel ($CHANNEL) includes '*/ubuntu-##.##' track per "
-        echo "Ubuntu policy (ex. stable/ubuntu-18.04) the publisher will need "
-        echo "to temporarily create the channel/track to allow fallback during"
-        echo "download (ex. stable/ubuntu-18.04 falls back to stable if the"
-        echo "prior had been created in the past)."
-        exit 1
-    fi
-
-    mv -v $seed_dir/*.assert $assertions_dir
-    mv -v $seed_dir/*.snap $snaps_dir
-
     # Add the snap to the seed.yaml
     ! [ -e $seed_yaml ] && echo "snaps:" > $seed_yaml
     cat <<EOF >> $seed_yaml