Have put a Samsung 860 QVO in a Thinkpad T520i and cloned old HDD to it.

If T520i is switched on via power button, SSD works perfect, Windows 7 Pro X64 boots up fine.

If a "Restart" is initiated within Windows, the SSD shows up in BIOS POST output as "Fixed Disk: Samsung 860 QVO 1TB", but directly after that it is not recognized (any more?), the bootmenu of Thinkpad with DVD drive only shows up. No other devices are connected, only PSU.

Any idea what's going on here?

SSD was updated to latest firmware with Samsung Magician during problem research, no change.

Have posted some more details with screenshots also here: hXXps://forums.lenovo.com/t5/ThinkPad-T400-T500-and-newer-T/Windows-does-not-see-boot-SSD-at-warm-restart-T520i/td-p/4624239

Thanks for any ideas how to fix that.