When you create a Line and Clustered Column chart, then add the following:
Shared Axis value
The Secondary Axis for the Y axis shows up. but if you go into the report settings, it shows the secondary is off. The fix is to "turn it on" which does nothing as it is already on, then turn it off. Then the secondary axis turns off.
This chart either should not show the secondary Y axis by default as the settings indicate, or the setting should be shown as "on." The user should not have to flip it on/off for this to take.
This is with the May 2020 desktop but was in at least the April version as well.