Maple flavor is strongest in mid-season maple syrup. Why? That's the question.
Ambient temperature rises throughout the season and affects some flavors more than others. The flavors that increase throughout the season could be because of greater fermentation of sap in the tanks and changes in the sugars. That could happen before boiling or changing compounds, which then are more susceptible to changes during boiling.
Soloton is the compound responsible for maple flavor in maple syrup. It's a lactone and an extremely powerful aroma compound, with the typical smell of fenugreek or curry at high concentrations and maple syrup, caramel, or burnt sugar at lower concentrations.
Unlike other aromatic compounds in maple syrup, production of sotolon peaks 70C, meaning it is not created at ambient temperature or while boiling. It happens in between. For comparison, vanillin is produced in collection system and sap tanks. Caramelization happens while boiling because of the Maillard reaction.
What could make maple flavor increase, peak, then drop? Hypothesis to test - if you have a preheater, you'll have sap/concentrate at or around 70 degrees longer than if you have put concentrate directly into the rear float box and rear pan. If you recently added a preheater, did you notice a change in the mid season flavor of your syrup?
Another hypothesis: if you tasted hyper-Brix sap (concentrate to 30+ Brix before boiling) did you notice a drop off in the maple flavor from what you would expect. That could be because the concentrate isn't in the 70C range long enough to develop soloton.