Teensy 4.1 low temperature - strange menory issues

[Uli]

Hi.
After only reading for all times, I registered today to ask a question about the Teensy 4.1.
This one Teensy 4.1 is dedicated to testing highly efficient Organic LEDs. The Teensy is powered by USB.
At higher temperature it works totally normal, as expected, and draws about 250mA.
During a low temperature test, the Teensy 4.1 started to show a strange behavior.
If the setup was left at 9°C air 45% RH for minimum 4 hours, the Teensy will not boot any more with the following code:

[...]
FLASHMEM
void setup() {
  //                            waiting, give everything time to start up
  delay (500);
  //                            all LEDs on
  for (b = 0; b < sizeof(LEDpin); b++) {
    pinMode(LEDpin[b], OUTPUT_OPENDRAIN);
    digitalWrite(LEDpin[b], 0);
  }
[...]

The low signals will never appear on the pins, instead they show a pulldown behaviour, and the Teensy 4.1 draws about 2A from the USB in random short pulses, but nothing on the teensy board heats up.

After power cycling, the cool Teensy red LED sometimes blinks series of two, or stays completely dark, or stays dimly lit with obvious darker flickering.
Once this strange behavior happened, the Teensy will never boot the code again, even after warming it up to room temperature.

Holding the Program Button on the cool Teensy while power cycling and keeping it pressed for about 30 seconds, does sometimes lead to a short red blip followed by very long >60s bright red, but the orange blink does not come up, even after power cycle. If the setup is rewarmed again, this restore procedure does work normally as expected.

If I change the FLASHMEM to FASTRUN, it boots and works normally, even in the cooled condition.

[...]
FASTRUN
void setup() {
  //                            waiting, give everything time to start up
  delay (500);
  //                            all LEDs on
  for (b = 0; b < sizeof(LEDpin); b++) {
    pinMode(LEDpin[b], OUTPUT_OPENDRAIN);
    digitalWrite(LEDpin[b], 0);
  }
[...]

I've also tried longer startup delay, but even two seconds do not give any different result.

What could this be?
The Teensy 4.1 is one of the first series.
Would a new Teensy 4.1 from the most recent production run solve the issue?

 

[Uli]

Additional info: This happens with Teensyduino 1.57 and 1.58b3, all in Arduino 1.8.19 on Win 10 x64

 

[Uli]

All right, got it.
Final info here:

Yesterday right before knocking-off I disassembled the complete setup.
The problem persists on the Teensy 4.1.
Teensy alone, with the recovered blink at room temperature: powers on, works
Teensy disconnected from USB, cooled, reconnected: Not work. Shows same behaviour like written in first post.
USB device faulty to OS.
Teensy warmed up again, reconnected to USB: Not work. Shows same behaviour like written in first post.
USB device faulty OS.
Warm Teensy button hold recovery: Works.
No USB device, but pressing button makes HID appear.
Repeat.

Side cutter.
Trash.
End of Teensy 4.1 story.