There seems to be a number of webmasters complaining that the Google Search Console's hreflang international reporting tool is showing errors and a drop in "known tags" in the report. Webmasters who have implemented them correctly are seeing 'no return tags' issues.
@SEO_Suedwest shared a screen shot of the chart showing the drop in known tags:
John Mueller from Google has been responding to folks on Twitter that he is looking into this:
@seoseb Not sure, but I'll take a look. Thanks!— John Mueller (@JohnMu) October 26, 2016
@SEO_Suedwest Thanks -- taking a look.— John Mueller (@JohnMu) October 26, 2016
I am @rustybrick, all software says we've implemented everything correctly but still getting 'no return tags' in GSC.— Cian Murphy (@CianMMurphy) October 26, 2016
I assume it is just a reporting bug and not a real bug that impacts your indexing and ranking in Google but we will learn more soon.
Forum discussion at Twitter.