The 5.3 kernel currently sets the upper USB 3 port to OTG mode, hence the USB drive dont show up.
Based on above report @mara created a patch for Slarm64:
I submitted it to Armbian and it got accepted:
So you can try switching to and testing latest kernel on Armbian using armbian-config (have not tested it myself, it can break your system). Or you can wait for next Armbian update to get the updated kernel. Another option is to rebuild Armbian kernel using Armbian build script.