Googlepages URLs to my old site are no longer redirected to Google Sites

For a couple of years, I maintained a "mirror" of my blog (hosted in my old account) on a free page hosted in Googlepages. Over the years, people started using links to that mirror instead of the primary site - and the Google bot learned about it, thus replying to queries with URLs that point to the ttsiodras.googlepages.com domain.

After a couple of years, Google announced it would migrate Googlepages to Google Sites, where people wouldn't be able to write their HTML/CSS/JS, and instead would use on online editor. I had no desire to spend any effort doing that, so I just (a) setup the redirection offered by Google, from the old URLs (ttsiodras.googlepages.com/whatever) to the new Google Sites page (https://sites.google.com/site/ttsiodras) and (b) had that Google Sites page contain direct links to my main page.

And it worked fine. Until now - or at least, until recently.

I checked yesterday, and found out that URLs to my old site (ttsiodras.googlepages.com) are now getting 404s, and are not redirected to Google Sites.

Did something change, recently, in the way these redirects work? Note that I checked some other googlepages links (not of my old site, of other peoples) and it appears they work.

Or was the redirection a temporary service offered by Google? (if so, I can't understand why - the resources involved in this are surely trivial for someone like Google).

Any hints/suggestions most welcome.