Unfortunately, there is no fixing your ubi. The problem is no longer with the Ubi software, it's below that. The problem is no longer with the Android OS, it's below that as well. The problem is with the hardware.
Connect the minipc to your pc and install the ADB software and have a look at the Android OS. Running the dmesg command will show things like this:
<6>[ 2.026515] lun0: LUN: removable file: (no medium)
<6>[ 2.031454] lun1: LUN: removable file: (no medium)
A LUN is a Logical Unit Number, or simply, a hard disk. There are 2 there and they are both missing. So, no hard drives, no ubi.
Further in the OS, in some of it's logs, you can see this (read from the bottom up):
<4>[136893.054477] [<c051b1c4>] (unwind_backtrace+0x0/0xf0) from [<bf009198>] (FlashReadErrorDump+0x9c/0xd0 [rk30xxnand_ko])
<4>[136893.065284] [<bf009198>] (FlashReadErrorDump+0x9c/0xd0 [rk30xxnand_ko]) from [<bf00a954>] (FlashReadEnhanced+0x16c/0x260 [rk30xxnand_ko])
<4>[136893.077812] [<bf00a954>] (FlashReadEnhanced+0x16c/0x260 [rk30xxnand_ko]) from [<bf00ce54>] (FlashCopyProg+0x1f8/0x360 [rk30xxnand_ko])
<4>[136893.159606] [<c0559dc0>] (kthread+0x80/0x88) from [<c0516678>] (kernel_thread_exit+0x0/0x8)
<4>[136893.181899] FlashReadRetry error!!,row = 556040
Looks like the Flash memory has failed, and a kernel thread has stopped.
On any other PC, if you get hard drive errors, you replace the hard drive. Since the hard drive is flash memory on the motherboard, you have to replace the motherboard. ie, buy a new ubi.
You can't fix it in software. There is nothing you can do.