UPDATE 8-12-21: It looks like this issue is back again. Sellers are reporting tracking numbers are not "sticking" once they upload them into eBay's system.
Update 6-14: Sellers are reporting this morning the defects have been removed and their seller level metrics have been restored to where they should be.
UPDATE 6-13: eBay has added a notification to the seller dashboard acknowledging the issue and stating sellers' benefits will not be affected.
Some eBay sellers are reporting receiving "tracking not uploaded" defects on their accounts for orders that show shipped with tracking in their Seller Hub records - some even purchased shipping labels directly from eBay!
There are also multiple posts on the eBay community about this issue.
It appears most reports are showing orders being affected on/around May 28- May 31st, with some speculation there could be an issue with eBay accounting for the Memorial Day holiday for "on time" shipping.
However, it's import to note the defect is not for tracking being uploaded late - it is saying that tracking was not uploaded at all, so it would seem to be a deeper technical problem than simply forgetting not to count the holiday as a shipping day.
There were reports of similar problems on May 17th, where tracking numbers were being uploaded, but were not visible to both buyers and sellers on some orders.
There has been no response from eBay staff in the community yet and the eBay System Status page shows no disruptions or outages, though it is not uncommon for the status page to show "all clear" even when there are known sitewide technical issues occurring.
I'll update as more information becomes available.