DIAGNOSIS The electric brake circuit has failed. This saw uses a dynamic brake that shorts the motor to stop it. The failure is internal.
FIX This is not a user-serviceable fix. The brake function is controlled by the switch assembly and the tool's electronics. The entire switch/controller unit must be replaced.
IF THAT DIDN'T WORK There is no secondary fix. A continuous spin-down is a sign of electronic component failure in the switch module.
HEADS UP This is a serious safety issue. Treat the saw as if it has no brake. Always wait for the blade to come to a complete stop before setting it down. Consider professional service.