Help! Sandisk Ultra Dual Drive USB Type-C Appears then Disappears

Hi everyone,

Going crazy and hoping to find some help!

I have a 2016 MacBook and loaded some documents onto my brand new SanDisk USB Dual Drive Type C flash drive.

I had been using it on my work computer (Windows 7, HP), with no issues. 

Plugged it into my macbook, and it recognised the USB drive, and I was able to open the folder it was in. I have some encrypted files in there, so I clicked “access encrypted files (mac).dmg” and the installer began. It then said successfully installed and we need to restart. Restarted the computer and now it won’t recognise the Sandisk flash drive anymore - if I plug it in, it recognises for a moment, then it disappears.

I’ve checked disk utility and system information and they both tell me that the drive is connected, but unmounted…

What have I done? Why can’t I access it? 

Please help!