Google has said it changed the error and issues reporting in Google Search Console for Breadcrumbs and HowTo structured data. This may result in new errors, warnings and issues or changes to the severity of the issues already reported by Google in Search Console's enhancement and rich results reports.
Google wrote that as of January 31, 2021 and going forward "Search Console has changed the way that it evaluates and reports errors in Breadcrumbs and HowTo structured data. As a result, you may see changes in the number of Breadcrumbs and HowTo entities and issues reported for your property, as well as a change in severity of some issues from errors to warnings."
So go into the rich results report and check to see if you have new or updated errors, warnings and issues for your Breadcrumbs and HowTo structured data - that is, if you implemented those structured data elements on your site.
Forum discussion at Twitter.
