ego power+ mower blade suddenly stopped spinning but the motor still runs, what gives?

The blade adapter hub or drive key has sheared.

1. Disconnect the battery immediately.
2. Inspect the blade, blade bolt (part number 5640321002), and the prevailing torque hexagon lock nut (part number 5630351002).
3. Remove the blade and check the fan (part number 3403110001) and the hub it mounts to for damage.
4. The hubcap (part number 3126769001) and related components on the motor shaft may be stripped.

If that didn't work, the issue is internal to the power unit (part number 2824285002). The motor shaft or the internal connection to the blade assembly has failed.

Heads up: This is a critical safety failure. Do not attempt to restart the mower until the cause is identified and repaired.