This displayed if the disk drive seems in sleep/standby state according the driver of the disk controller (probably the chipset). Then Hard Disk Sentinel does not access it to just to detect its status in order to minimise power use.
Some disk controllers/chipsets (more precisely its driver) may provide this information incorrectly. Not sure, but this can happen in your case too.
I recommend to please use Report menu -> Send test report to developer option, as then it is possible to check the actual situation, examine the combination of the controller + driver + the SSD and verify if/how things can be improved: for example by an updated driver and/or by handling this situation differently.