make flash; A fatal error occurred: Timed out waiting for packet header

[semireg]

I'm trying to flash a custom firmware. This is actually a successful flash, but it ends with an error of gloom and doom.

Any ideas what could be causing this false alarm? I'm able to flash the firmware using "Pycom Firmware Update".app on Mac OS without error.

I'm running this from a Ubuntu VM on Mac OS. I haven't had issues with flashing ESP8266s from this VM.

$ make flash
Use make V=1 or set BUILD_VERBOSE in your environment to increase build verbosity.
Entering flash mode
Flashing project
esptool.py v2.1
Connecting.....
Chip is ESP32D0WDQ6 (revision 1)
Uploading stub...
Running stub...
Stub running...
Changing baud rate to 921600
Changed.
Configuring flash size...
Auto-detected Flash size: 8MB
Flash params set to 0x023f
Compressed 16320 bytes to 10584...
Wrote 16320 bytes (10584 compressed) at 0x00001000 in 0.1 seconds (effective 1021.0 kbit/s)...
Hash of data verified.
Compressed 3072 bytes to 133...
Wrote 3072 bytes (133 compressed) at 0x00008000 in 0.0 seconds (effective 1541.5 kbit/s)...
Hash of data verified.
Compressed 1180128 bytes to 778556...
Wrote 1180128 bytes (778556 compressed) at 0x00010000 in 13.1 seconds (effective 722.6 kbit/s)...
Hash of data verified.

Leaving...
Staying in bootloader.

A fatal error occurred: Timed out waiting for packet header
application.mk:423: recipe for target 'flash' failed
make: *** [flash] Error 2

Again, this indeed succeeds as far as I can tell... the expected code runs on the device.