Google updated the Search Console rich results report for breadcrumbs starting on June 8, 2023. The report now shows warning when sites use the HTML id attribute to specify an ID for Breadcrumb structured data. This may result in an increase in warnings within that Breadcrumb report.
Google posted about this in the data anomalies help page with the date of June 8, 2023. It says, “Search Console started to show a warning when sites use the HTML id attribute to specify an ID for Breadcrumb structured data. As a result, you may see an increase in warnings in your Breadcrumb report. See the Breadcrumb documentation for more information on how to specify IDs.”

So if you see a spike in warnings in that Breadcrumb report, that is why.
A breadcrumb trail on a page indicates the page’s position in the site hierarchy, and it may help users understand and explore a site effectively. A user can navigate all the way up in the site hierarchy, one level at a time, by starting from the last breadcrumb in the breadcrumb trail.
Google’s Ryan Levering added on Mastodon, “Apologies to everyone for the awful error in the console. It says “missing id” when it’s actually “itemid” that’s missing. We just don’t have a syntax specific message right now.”
Forum discussion at Mastodon.
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