Please try reformatting your USB flash disk using the procedure described in link below. You'll have to re-run UniBeast afterwards, making sure that the two checkboxes in Post #3 above are turned on. The root cause of your problem seems to be that two separate disk partitions were not created on the USB flash disk. So the link below should help to create those two partitions.
https://www.tonymacx86.com/threads/solved-error-loading-operating-system.266874/#post-1867240
Good catch!
- The uploaded image shows an 8GB Flash disk FDisk_Partition scheme and not the usually recommended 16GB FD in GUID Partition scheme for Mojave USB Installer Creation.
- I suspect the problem must have occurred at the Disk Utility >Erase Step