SSD Extreme Pro Not Ejected Properly / Not Recognized

Hi everyone,

I bought a new SanDisk Extreme Pro SSD 2TB, reformatted it for Mac in Mac OS Extended Journaled, and all seemed working fine.

But I notice now, always after rebooting the computer the SSD is not recognized, and a notice is showing up, ‘Disk has not been ejected properly’. When I unplug und plug in again the USB cable, it is showing up normally.

Why this is happening? I also have an older SanDisk Extrem Portable 2TB connected, but this one is showing up normally after rebooting.

I am somehow disappointed, I hope someone can help me to explain, what is the reason for that.

Thank you