my SSDSC2BW240H601 was working fine for almost a year in a mostly idle Ubuntu 16.04 system. Recently it started misbehaving:
For no apparent reason it would just disappear and on subsequent system restart BIOS will fail to enumerate device or it will be presented as sandforce.
Sometimes it does manage to initialize correctly and by looking at the report from Intel's SSD Toolbox it's health status is OK, and as far as I can tell it is running latest firmware - RG21.
We understand your situation regarding your Intel® SSD 535 Series.
Based on the information provided, it seems that the controller inside of your SSD may be failing.
In order to better address this problem we can recommend for you to contact your local support team to verify the warranty information for your drive, which may need to be replaced.