Thanks for your message.
Sorry for the possible issue, but of course NO, there is absolutely no bug/problem with the software.
> I think it's probably the power / cable and the drive is fine
Yes, I completely agree, I also think so.
Of course if the drive is not responding (for example by a cable/connection issue), it is completely normal and expected that
- the disk test window (generally any software which attempts to access the disk) seems not responding "hung" while waiting for the device
- after some time, the device may disconnected, disappears from Windows Explorer
- all further disk access attempts are invalid, so the remaining blocks are RED, to confirm that there was an error during the test. The bottom of the test window likely displayed the problem/error, for example "The disk/resource is no longer available" or similar, to suggest that the disk is no longer connected.
But this is not a bug of Hard Disk Sentinel of course, it works completely as expected: just when it lost the communication with the drive, it can't perform/continue of course.
In some situations, the USB adapter/enclosure may overheat and got stuck (happens if used intensively, for example to test disk(s) for longer time).
Yes, if such happens, it is good idea to re-run the test, to verify the situation - or confirm if the drive is generally working correctly.