It is still good. Issues that could have caused it not to seal, something on the rubber part of the lid, temperature of the syrup not hot enough or something on the top surface of the jar. There could be other causes too. Just be glad you found it early. Put it in the fridge and use it next.
As long as the syrup was at proper density, maple syrup does not "go bad". It may get some mold on top, but if some ever does, heat it back up to 180-190F, skim the mold off and the rest is good.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.