Hi Dave,
I'm Sumit, here to help with your query in the Microsoft Q&A.
Apologies for any inconvenience you are experiencing. I am happy to help you today.
There were some glitches on the device page last week, where some devices disappeared automatically despite everything being correct. I wonder if the same bug is still present and Microsoft has not yet fixed it.
You can get all the keys from https://aka.ms/myrecoverykey page. They remain even if the machine is deleted. That is not an issue.
Moreover, you can also backup the key to a file from Control Panel > Manage Bitlocker > Save recovery key.
I look forward to your response and am happy to work with you until we find a solution. Please keep me updated.