This thread is very interesting.
I have my own Samsung 860 EVO solid state disk (500 GB) that worked fine for 2 years in my Windows 8.1 desktop computer.
Suddenly something happend in the night when I was sleeping (the PC was in the SLEEP mode as well

)
After this unexpected event the drive is not dropping the BUSY flag, the only ATA command that is executinging is IDENTIFY DEVICE.
All other commands result in the constant BUSY state, but if I disconnect and reconnect the SATA cable the BUSY flag is dropped and the drive reports to be ready again (with both DRDY and DRSC flags being raised, and BUSY flag dropped).
I suspect it may be caused by the damage of the voltage regulator chip on the SSD disk's PCB.
Any ideas?
How to diagnose this problem?
The gurus advice will be very much appreciated!