This anomaly applies to Revision 2, build codes CKAA-Dx0, QIAA-Dx0.
Full flash erase through CTRL-AP is not successful.
WDT is enabled.
Flash is not erased. If the device has a WDT time-out less than 1 ms and is readback-protected through UICR.APPROTECT, there is a risk of permanently preventing the erasing of the flash.
Try again.