SerialUSB and STM32F103C8 dont work anymore

I have started a new project. (PlatformIO Core 6.1.11 Home 3.4.4)

platform = ststm32
board = genericSTM32F103C8
framework = arduino
debug_tool = stlink
upload_protocol = stlink
monitor_port = COM31
monitor_speed = 115200

lib_deps =

build_flags =

;monitor_dtr = 1

Uploaded this small code to the Bluepill:

#include <Arduino.h>

void setup() {
// put your setup code here, to run once:

void loop() {
// put your main code here, to run repeatedly:


With the above .ini and small code, I can’t connect to the USB port
If I upload an older code to the same board, the USB port works fine.

What can I do to make the USBSerial work again ?

Thanks in advance
Jens Larsen

SOLVED… I hope!!!
An USB Isolator behaved very unnormal.
But I don’t understand why it works with older codes :space_invader: