Earlier this month, Google had announced that they are going to stop supporting no-index directive in Robots.txt files. Google had been telling webmasters and SEO experts not to use this for years. They had announced that they will not honor any crawl-delay, no-follow, and no-index mentioned in your Robots.txt file from September 1st, 2019.
Google said they might send notifications to you regarding the same via Google Search Console. Well, they are doing it now. Here is a couple of screenshots from Twitter.
The notice reads, ‘Remove “no-index” statements from the robots.txt of http:’ Some people have received many notices. Maybe Google was suffering from an alert delay.