Why does Offload say my fast drive isn't connected?

Short answer: Offload copies the app to your fast drive, so the drive must be connected. Reconnect it and try again — nothing was changed.

Offloading copies the app and its data to your fast drive, so the drive has to be plugged in and set up. Reconnect it and click Offload again.

Nothing was changed when you saw the message — the app is still on your Mac.