DIAGNOSIS The blade attachment system is failing. The most common culprit is a worn or missing O-ring on the blade bolt.
FIX Inspect the flat black O-ring on the bolt shaft. If it's cracked, flattened, or gone, replace it. DeWalt part number N472377. Clean the tool's blade mount and the blade itself of all sawdust and debris before installing.
IF THAT DIDN'T WORK The star washer inside the blade mount might be damaged or packed with debris. Remove the bolt and inspect the serrated washer. Clean it or replace it (DeWalt part N472378).
HEADS UP Do not use thread locker or excessive force on the bolt. You can strip the threads in the aluminum housing. Hand-tighten firmly with the provided wrench.