"libusb: error [_get_usbfs_fd] libusb couldn't open USB device"

[unimatrix099]

On Ubuntu 16.04, latest rkflashkit version from the github as root
Device RK3188 is detected:

============= 2018-10-01 13:52:31 ============

Loading partition information
MACHINE_MODEL:rk3188
MACHINE_ID:007
MANUFACTURER:RK30SDK
MAGIC: 0x5041524B
ATAG: 0x60000800
MACHINE: 3066
CHECK_MASK: 0x80
KERNEL_IMG: 0x60408000
#RECOVER_KEY: 1,1,0,20,0
CMDLINE:console=ttyFIQ0 androidboot.console=ttyFIQ0 init=/init initrd=0x62000000,0x00800000 mtdparts=rk29xxnand:0x00002000@0x00002000(misc),0x00006000@0x00004000(kernel),0x00006000@0x0000a000(boot),0x00010000@0x00010000(recovery),0x00020000@0x00020000(backup),0x00040000@0x00040000(cache),0x003FE000@0x00080000(userdata),0x00002000@0x0047E000(metadata),0x00002000@0x00480000(kpanic),0x00180000@0x00482000(system),-@0x00602000(user)

Error in console when running any partition operation:

libusb: error [_get_usbfs_fd] libusb couldn't open USB device /dev/bus/usb/001/052: No such device
Traceback (most recent call last):
File "/usr/share/rkflashkit/lib/rkflashkit/main.py", line 275, in __flash_image_file
op = rktalk.RkOperation(self.__logger, device_info[0], device_info[1])
File "/usr/share/rkflashkit/lib/rkflashkit/rktalk.py", line 102, in init
self.__dev_handle = device.open()
File "/usr/share/rkflashkit/lib/rkflashkit/usb1.py", line 1622, in open
raise libusb1.USBError(result)
rkflashkit.libusb1.USBError: LIBUSB_ERROR_IO [-1]
^CTraceback (most recent call last):
File "/usr/bin/rkflashkit", line 21, in
app.main()
File "/usr/share/rkflashkit/lib/rkflashkit/main.py", line 421, in main
gtk.main()

Any ideas on why this error or how to debug this issue?