As of January 19, 2023, Google has updated the video indexing report in Google Search Console, which now reports on thumbnail indexing issues more accurately. The result may be that you see reassignment of "Missing thumbnail" issues to more specific issue types, Google said.
Google posted this on the data anomalies page and wrote, "Search Console can now more accurately classify thumbnail indexing issues. As a result, you may see a reassignment of "Missing thumbnail" issues to more specific issue types. The total number of affected videos should remain the same."
So if you see that the number of issues reported in total are the same, that means there are no new errors but the errors may have been reassigned to a different type of error.
Google has a detailed help document on this report explaining all the errors and their meanings.
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