Short SMART test succeeds, extended SMART test fails

Sandisk SSD Dashboard version

Running SMART disagnostic short test succeeds with no errors.

Running SMART diagnostic extended test reports only “failed”. Progress bar shows 10% then 20%, never got to 30%. Problem is repeatable, including after fresh reboot with no user apps running.

Report generated but cant’d be attached (posting only permits .jgp/.gif/.png)

How do I figure out what is wrong? (System is and had been running fine, no obvious issues.)

Thanks for any pointers.