Hope this resolves the issue for you!Ghl recommends as a common step in the troubleshooting documentation to use the "prepare measurement cell" function, and wait at least 6 hours.
I just did that since it can be done remotely with myGHL.
Seems like air bubbles is the bane of the IonD, and extra care needs to be taken to avoid them.
Preparing the measurement cell will flush the system, and hopefully evacuate air bubbles.
I'll see how that went tonight at my usual 8pm measurement.