I had the same problem and fixed it by adding the following line to platformio.ini (below the [env: ] line:
extra_scripts = post:extra_script.py
Then adding a file named extra_script.py in the same folder as platformio.ini containing:
Import("env")
def after_upload(source, target, env):
print "Delay while uploading..."
import time
time.sleep(2)
print "Done!"
env.AddPostAction("upload", after_upload)
The amount of time to wait is specified in the time.sleep(x) command, 2 seconds worked for a Teensy 3.6 project that’s about 300k of downloaded data. You can adjust as needed.