Google has updated its Get On Discover page in the RSS feed for the Follow feature in Google Discover section to specify the most important content for that section. Google added that the "most important content for the Follow feature is your feed title element and your per item link elements."
This is the new line that Google added, "The most important content for the Follow feature is your feed title element and your per item link elements. Make sure your feed includes these elements." Prior to yesterday, that line was not there.
So if you are using this feature, make sure to include those two elements of content in your feed.
Forum discussion at Twitter.