Email dissppeared from inbox

When I reply to an email, this reply also appears in my inbox, BUT the original message has disappeared from the inbox

You are looking at a conversation. So the original received message as well as your reply. If you scroll up in the message preview, you will see the original received message.

If you would rather not use conversations, you can disable them by selecting Menu > View > Conversations > Disable Conversations.

Seems to work.
Thank you