Summary:
The new label system is charging the Commercial Base rate for all Priority Mail labels, even for Top Rated Sellers who should be paying the Commercial Plus rate.
The linked thread includes screen shots of label prep pages for the same package, with the same weight, addresses, etc., using the old and new label forms, for which the OP, who is a TRS, was charged the Commercial Base rate when using the new form.
The link in the OP for this thread isn't working for me, so here's another link to the same thread:
https://community.ebay.com/t5/Shipping-Returns/Difference-in-shipping-cost-between-new-and-old-label...
Also see post #22 in this thread. The seller is charged the Commercial Base rate rather than the Plus rate, And the form also reflects the Base vs Plus rate for the automatically-included insurance ($50 vs $100).
https://community.ebay.com/t5/Shipping-Returns/New-shipping-labels-page/m-p/28714811#M246236
