eBay Places Restrictions on USPS Media Mail
UDPATE: eBay has posted an announcement telling sellers to disregard the original emails
Earlier today, an email concerning Media Mail was sent to some sellers (subject: “USPS Media Mail isn’t available for some categories”). Sellers who received the email should disregard it.
No changes are being made to categories that are eligible for printing labels with Media Mail at this time and you do not need to take any action.
We apologize for any inconvenience this may have caused you.
As always, thank you for selling on eBay,
Your Selling Team
UPDATE: According to eBay community staff - the email in question included incorrect categories and/or listings and corrected emails will be sent out "soon".
We've heard back that the email included incorrect categories and/or listings. Given the USPS determines the eligibility of items that may be shipped using Media Mail - the email was intended to provide a heads up of sorts, for any sellers that may have been offering it incorrectly. We're not blocking any new/additional categories though, and you can expect to receive a corrected email soon. Thanks!

Sellers are reporting receiving emails from eBay notifying them of new restrictions on shipping via USPS Media Mail.
The message from eBay states:
Your account has active listings that offer USPS Media Mail as a shipping service option in categories that aren’t eligible for Media Mail under USPS rules. In addition,eBay Labels does not support shipping label printing for Media Mail in these categories.
In order to prevent buyers from selecting Media Mail for listings that aren’t eligible for the service, we recommend you update your active listings to remove Media Mail as a shipping service option for items in those categories. For new listings in those categories, Media Mail won’t be an available shipping service.
Below is a summary of the top categories in which you have the most active listings. Please note that you may have active listings in additional categories:


There is a lot of confusion as sellers believe some of the categories affected do qualify under the USPS Media Mail Guidelines

Sellers have been reporting being blocked from purchasing media mail labels for months, but previously eBay staff had indicated it was a glitch that they were working on correcting - that apparently doesn't seem to be the case.

I'll update this post as more information becomes available.