I moved this blog to a custom domain about two months ago. Blogger makes the process very simple if you already own your own domain. I was up and running at blog.coditate.com after just a few clicks in the Blogger dashboard, and adding a new CNAME record for this domain.
A short time later I realized all the comments were missing from this blog. Apparently this has been quite a problem for months and based on the hundreds of unanswered complaints in the Blogger help forum, Google hasn't been very responsive or helpful in explaining why this happens or how to fix it.
Following the advice on this thread, I switched back to my old blogger-hosted address and the old comments reappeared. However, all new comments added since the domain switch had now disappeared. I switched back to my custom domain. Now both the old and new comments were gone!
Finally, after a couple more switches between my custom domain and blogger-address, all comments--both old and new--reappeared at once and seem to be sticking around. But the unreliability and lack of support from Google are not exactly confidence inspiring. In fact, it's downright scary when I think about how much of my important data is spread across Google's free services.