KCDW, sorry for belated reply
Two theories:
(1) stuck throttle valve. Another pilot had suffered a power failure and recovery on final a few weeks previously. When the engineer arrived some hours after the landing, he replicated the power loss on his first two attempts to run the engine. Then it ran normally.
(2) carb ice. Odd, this, as we were flying circuits, and had just completed a full power climb, in ambient conditions which were not particularly conducive to carb ice. The EGT needle was not in the arc in which carb ice is likely.
It turned out that aircraft needed a new engine shortly afterwards, when an inspection revealed a (different) major problem.