We have had this problem chronically sinse we started years ago. The principal noted above about letting the microbes do there thing to make the different sugars that
carmelize and darken the syrup and make stronger flavor sounds good. We tried it a couple of times and for reasons we can't explain, our bacteria/microbes gave us a batch of nice light "ropy" syrup. It's worth a try but your mileage, like ours, may differ. If you get into the ropy stuff, there is no know recovery. The only remedy is to dump it, and all the sap and vigorously clean everything that has been exposed to it.
Big loss of syrup.
Big loss of time.

Oh and all the customers that sought us out and come up the driveway want "real" maple flavor, with gusto. Very frustrating.