Does anyone know why QBO suddenly decided that we should go back to paper mailing out a remittance advice? This seems absolutely ridiculous.

To support the postal service perhaps.

Jokes aside, there is a workaround per this thread: 

https://quickbooks.intuit.com/learn-support/en-ca/other-questions/re-seems-qbo-advanced-has-done-a-weird-update-and-we-can-no/01/1337000 

Good evening, laram-grinde-gma

It's great to see you in the Community, Welcome! QuickBooks Online is a powerful program that can help you keep track of your finances. I would be happy to guide you in the right direction for the best assistance possible.

In addition to the information provided above, I recommend clearing your cache and cookies, or trying a different browser, as it may be browsing data that is preventing the software from doing what it is supposed to do.

If the issue persist, I encourage you to reach out to the support team outside of the Community. They'll be able to verify your account details in a secure setting, as well as view your screen to better assist you. They also have the appropriate tools to create a ticket to get the issue resolved, if they feel it is necessary. You can reach them by following one of these methods:

Schedule a Callback or start a Chat: click (?)Help in the upper right > type and enter "Contact support" into the QB Assistant > click Contact Us > explain your situation > click Let's Talk > choose Get a callback or Start a Chat.
Social Media: Facebook and Twitter

If you have any other questions, feel free to reach out here.