DIAGNOSIS That's the saw telling you it's overheated. The M18 FUEL's electronic protection kicked in to save the motor and battery from damage.
FIX First, turn the saw off and set it down. Let it sit for a good 15-20 minutes to cool down completely. While it's cooling, check the blade. Make sure it's sharp, clean, and not pinched in the material. A dull blade or a bind makes the motor work way harder. After it's cool, try a lighter, free-running cut to see if it operates normally.
IF THAT DIDN'T WORK If it still blinks after cooling, the issue might be with the battery communication. Try a different, fully charged M18 HO (High Output) battery if you have one. The saw needs a lot of power, and a weak or older battery can trigger faults.
HEADS UP Pushing material too fast, especially through hardwoods, is the most common cause of this. Let the blade speed do the work. If you're getting this fault often, it's a sure sign you need to slow your feed rate or check your blade.