I have a Teensy 3.2 and wanted to try it out for the first time. Got the code to blink the LED and made 2 changes in the delay values to make a distinctly different blink pattern. I plugged in the Teensy, it started blinking. Opened up Teensyduino, set the board to "Teensy 3.2/3.1", put in the code, clicked the arrow to compile and download. Teensy Loader came up with a picture saying to press the button. I did that and the picture changed to show the Teensy and a progress message about downloading. But then "Download Error." I unplugged it.

Now the board appears bricked. It no longer blinks at all when I plug it in. It does not show up in the System Report of connected USB devices. Teensy Loader no longer displays the picture saying to press the button. Trying to download the sketch again and Loader just says "Erasing" then "Download Error." Clicking Reboot gives "Unable to reboot."

Thinking I might have a bad board I foolishly tried it again. Same sketch, same procedure but this time with a Teensy LC. Got the same result, another apparently bricked board. I've tried this a few times with each board but the same results.

I'm using Teensyduino 1.53 (Arduino 1.8.13) and Teensy Loader 1.53.
Macintosh MacBook Pro Touchbar. Mac OS 11.4.
Connecting with a powered USB hub that plugs into USB C on the Mac and has several USB type A jacks.
No power supply or other hardware connected.

I've tried holding the button for 15 sec at power on but that didn't seem to do anything.

Here's the code:
Code:
/*
  Blink

  Turns an LED on for one second, then off for one second, repeatedly.

  Most Arduinos have an on-board LED you can control. On the UNO, MEGA and ZERO
  it is attached to digital pin 13, on MKR1000 on pin 6. LED_BUILTIN is set to
  the correct LED pin independent of which board is used.
  If you want to know what pin the on-board LED is connected to on your Arduino
  model, check the Technical Specs of your board at:
  https://www.arduino.cc/en/Main/Products

  modified 8 May 2014
  by Scott Fitzgerald
  modified 2 Sep 2016
  by Arturo Guadalupi
  modified 8 Sep 2016
  by Colby Newman

  This example code is in the public domain.

  https://www.arduino.cc/en/Tutorial/BuiltInExamples/Blink
*/

// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(100);                       // wait for 0.1 second
  digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
  delay(3000);                       // wait for 3 seconds
}