No USB on overclock, V4.4.4

[Macrosii]

Hi
In trying to debug an issue with PSRAM and overclocks, I find I am having issues with USB output.
For the following code I get no USB at a 240MHz overclock with Pico SDK selected. With TinyUSB I do get an output.
Apologies if I am doing something stupid.
Raspberry Pi 5,8GB, 64GB Bookworm
IDE 1.8.19
Core 4.4.4
Adafruit Feather 2350 HSTX with PSRAM

Code

/*
  Blink without Delay

*/

#ifdef USE_TINYUSB
#include <Adafruit_TinyUSB.h>
#endif

//#define PSRAM_CUSTOM_SYSHZ 240000000 // let the peram know the spped of the CPU

// constants won't change. Used here to set a pin number:
const int ledPin =  LED_BUILTIN;// the number of the LED pin

// Variables will change:
int ledState = LOW;             // ledState used to set the LED

// Generally, you should use "unsigned long" for variables that hold time
// The value will quickly become too large for an int to store
unsigned long previousMillis = 0;        // will store last time LED was updated

// constants won't change:
const long interval = 1000;           // interval at which to blink (milliseconds)

void setup() {
  // set the digital pin as output:
  pinMode(ledPin, OUTPUT);
  Serial.begin(115200);
}

void loop() {
  // here is where you'd put code that needs to be running all the time.

  // check to see if it's time to blink the LED; that is, if the difference
  // between the current time and last time you blinked the LED is bigger than
  // the interval at which you want to blink the LED.
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis >= interval) {
    // save the last time you blinked the LED
    previousMillis = currentMillis;

    // if the LED is off turn it on and vice-versa:
    if (ledState == LOW) {
      ledState = HIGH;
    } else {
      ledState = LOW;
    }

    // set the LED with the ledState of the variable:
    digitalWrite(ledPin, ledState);
    Serial.println("Loop");
    Serial.print("CPU Freq");
    Serial.println(rp2040.f_cpu());
    Serial.print("PSRAM size");
    Serial.println(rp2040.getPSRAMSize());
  }
}