Flashing Nucleo L073RZ using CMSIS pack is unstable

Target: Nucleo L073RZ
OS: MacOS 10.14.5
Mbed OS: 5.13.1
Binary: mbed-os-blinky (built with GCC or AC6)

Flashing the above target using a specified CMSIS pack sometimes works, but more often claims No cores were discovered!.

Using the pack from here

./pyocd  flash --frequency 1800000 --uid 066DFF555654725187095153 --target STM32L073RZ --pack "/Users/thegecko/Desktop/Keil.STM32L0xx_DFP.2.0.1.pack" --erase=chip "/Users/thegecko/Mbed Programs/mbed-os-example-blinky/BUILD/NUCLEO_L073RZ/ARMC6/mbed-os-example-blinky.bin"

[====================] 100%

Then again:

0001326:WARNING:cmsis_pack:Page size (1024) is larger than sector size (128) for flash region IROM1; reducing page size to 128
0001775:WARNING:rom_table:Invalid coresight component, cidr=0x0
0001775:WARNING:rom_table:Warning: ROM table @ 0xf0000000 has unexpected CIDR component class (0x0)
0001776:CRITICAL:__main__:No cores were discovered!
Traceback (most recent call last):
  File "/Users/thegecko/mbed-studio-tools/python/lib/python2.7/site-packages/pyocd/__main__.py", line 338, in run
    self._COMMANDS[self._args.cmd](self)
  File "/Users/thegecko/mbed-studio-tools/python/lib/python2.7/site-packages/pyocd/__main__.py", line 468, in do_flash
    with session:
  File "/Users/thegecko/mbed-studio-tools/python/lib/python2.7/site-packages/pyocd/core/session.py", line 287, in __enter__
    self.open()
  File "/Users/thegecko/mbed-studio-tools/python/lib/python2.7/site-packages/pyocd/core/session.py", line 367, in open
    self._board.init()
  File "/Users/thegecko/mbed-studio-tools/python/lib/python2.7/site-packages/pyocd/board/board.py", line 83, in init
    self.target.init()
  File "/Users/thegecko/mbed-studio-tools/python/lib/python2.7/site-packages/pyocd/core/coresight_target.py", line 158, in init
    seq.invoke()
  File "/Users/thegecko/mbed-studio-tools/python/lib/python2.7/site-packages/pyocd/utility/sequencer.py", line 201, in invoke
    resultSequence = call()
  File "/Users/thegecko/mbed-studio-tools/python/lib/python2.7/site-packages/pyocd/core/coresight_target.py", line 238, in check_for_cores
    raise exceptions.DebugError("No cores were discovered!")
DebugError: No cores were discovered!

I've been unable to debug this board with a standard blinky example.

Start by reproducing the command against the Nucleo L073RZ with the specified CMSIS pack, then read pyocd/core/coresight_target.py around check_for_cores and the cmsis_pack and rom_table warnings. Done means identifying and fixing the intermittent “No cores were discovered!” failure and confirming that the blinky binary can be flashed and debugged reliably.