I can reproduce the problem when building a dummy package that build-depends on chromium-browser in a PPA.
Laney suggests that setting SNAPPY_STORE_NO_CDN=1 in the image build environment might help (this is done in livecd-rootfs).
In any case, it would be a good idea to update the ubuntukylin seeds to include the snap instead of the deb.
I can reproduce the problem when building a dummy package that build-depends on chromium-browser in a PPA.
Laney suggests that setting SNAPPY_ STORE_NO_ CDN=1 in the image build environment might help (this is done in livecd-rootfs).
In any case, it would be a good idea to update the ubuntukylin seeds to include the snap instead of the deb.