Omnichannel email conversation is empty and does not show up in queue

I had a test instance of RC on version 3.9.0 that I upgraded to 3.17.1 to test the email inbox feature of omnichannel.
I am not using omnichannel so far so I enabled it, added myself as a manager and an agent, and configured an email inbox. I haven't configured or tried any other channel.

When I send an email to the configured inbox:

• The chat appears in the list of current chats in the omnichannel settings
• The contact appears in the list of contacts of the contact center
• The chat DOES NOT appear in the list of chats in the contact center
• The chat DOES NOT appear in the queue
• If I open the chat from the current chats, the preview is empty, as if I has sent and empty email (which of course I didn't). If I click "Take it", the chat is still empty, and I cannot reply to it, but it does show up in my queue and I can post messages to the channel (that are not sent back to the contact, as expected).

I have tried this both without setting up any department, and with setting one up and assigning it to the inbox and the agent, same outcome.

What may I have missed in setting this up?

Reproduce the configured omnichannel email inbox flow described in the issue, checking current chats, the contact center list, the queue, and the conversation preview. Trace the email ingestion and queue-assignment entry points to find where the message content or visibility is lost; done means the conversation appears with its content and replies reach the contact.