Sandisk 32GB Extreme USB 3.0 mac boot

Hy everyone, I hava a brand new Sandisk 32GB Extreme USB 3.0 that i bought to run mac osx on my new imac that has a slow hdd.

I usally run perfectly os in usb drives but this new flash drive has a little problem!!! When  I turn on or restart the mac with the flash drive plugged-in the machine doesen’t recognize it and I have to unplugg and plug in agin the drive after this the dirve works fine.

Can anyone help me, do you know how to solve it?

Perhaps you can make this USB as bootable but other than that, I am not sure if this falls onto Sandisk support though.