I tried to create a new shipping label earlier, but eBay kept redirecting me to something that looked like the Shippo new account page.
As someone with an existing account, I knew to look under the existing menu items in Shippo and I saw that the eBay auth token had expired. I did not do anything to cause this to expire and I am unsure how long they usually last. I clicked the red button to reauthorize and then things started working OK.
Someone who is less technically proficient would have no idea what was happening based on (a) no error codes being displayed anywhere and (b) no information displayed that you already have a Shippo account and just need to reauthorize the eBay token.
Please look into addressing this issue for your other customers.