The lens correction feature has gone missing from the Development Module. It was missing before I upgraded to 5.6 and is still missing. Previously, it was present, so I am wondering if I did anything to hide or remove it?
Right-click on one of the other section headings, such as Tone Curve, Basic, etc. Make sure there is a checkmark in lens corrections. This is how you control which develop features you want displayed on your system. Sometimes features disappear mysteriously.