analogRead() freezing on several Trinkey boards

[caternuson]

Test sketch:

int count = 0;

void setup() {
  Serial.begin(9600);
  while (!Serial);
}

void loop() {
  Serial.println(count++);
  if (count > 5) {
    Serial.println(analogRead(A1));  
  }
  delay(1000);
}

Mixed results on several Trinkey products:

• PID 4870 - Adafruit NeoPixel Trinkey M0 (SAMD21) freezes
• PID 4964 - Adafruit Rotary Trinkey M0 (SAMD21) freezes
• PID 5020 - Adafruit NeoKey Trinkey M0 (SAMD21) freezes
• PID 5021 - Adafruit Slide Trinkey M0 (SAMD21) works
• PID 5022 - Adafruit ProxLight Trinkey M0 (SAMD21) works

Example output for sketch that works (PID 5022):

Example output for sketch that freezes (PID 4870): NOTE - closing Serial Monitor requires resetting the board