Check tube error on resmed

My s8 elite II gave me a check tube
Error last night. Tube seems fine. Any advise?

Per the User Manual: Troubleshooting:

Problem: Display error message:
Check tube!!
Key if done

Possible Cause: The air tubing is loose or blocked.

Solution: Check that the air tubing is connected securely to your mask and the air outlet on the front of the [machine]. When you have checked the air tubing, press the Start/Stop key to restart the device. If this does not clear the message, disconnect the power cord and then reconnect it to restart the device.

The machine "sensed" either excessive airflow (with no breathing patterns - that would have triggered a "high leak" message - leading to the assumption that the tubing was disconnected somewhere) or no airflow (not an apnea - even if you are not breathing there would be venting airflow through the mask - but it could possibly be the result of mask vents being blocked). If this recurs repeatedly without any cause, the machine may need to be serviced.

IF you took the mask off first, before you turned the machine off, the unit will give you the same message. Most of the time this is what has happened. The message resets itself everyday at midnight.