I'm just going out on a limb here and say this is likely your fault.

Large Letter = untracked you cant prove it.

Not uploading tracking in time you will be protected if ebay is asked to step in, providing you have a tracking update? Do you read seller updates cause I'm certain this is still valid today. https://sellercentre.ebay.com.au/2020-spring-seller-update/importance-of-tracking