When I go to MyHomey (https://my.homey.app/) all I get is ‘You do not have any Homeys’. I’ve no idea when thie device vanished, although it is haply running on my phone.
How do I get the web app to include the device?
Maybe log out of all Homey related apps and sites, and log on again? Just a long shot.
For me it looks like you have two accounts.
Check your account and email address from the mobile app and register your Homey id from there.
Log on in web app using the same account.
If your Homey is disconnected from your account send an diagnostic report from the mobile app to Athom and create a support ticket with the diagnostic id, your Homey id and your email address. And wait for their response.