How to program a BSFrance LoRA32u4 from Arduine IDE 8.5?
I've had the same problem, but couldn't fix it with the "Upload using programmer".
Instead i sound that the problem was that the serial connection kept dropping after a couple of seconds. My colleague, also on Ubuntu, had the same issue.

This fixed it for me: https://learn.adafruit.com/adafruit-arduino-ide-setup/linux-setup#udev-rules

The board registers as an Adafruit board on my system, and apparently the ModemManager is not too keen on that. 

After running first command in the link and restarting, i could upload to the board from Arduino IDE with no errors.