Silent, feedbackless failure of version regrade from Trisquel 8

Software Updater began offering Trisquel 9 to me only in December, after 8 had been desupported. When I selected it, the window disappeared, and nothing replaced it.

I think that I was exercising the update problems connected to https://trisquel.info/en/forum/repository-does-not-have-release-file#comment-163030.

Is it a fault that no error is shown to the user?

Until Trisquel 10 comes out, I have no plan for testing whether Trisquel 9 has the same behaviour. If people have an easy, nondestructive testing plan, then I am open to following it.