Faulty STM32 chip or incorrect core code

[brightproject]

Good day @fpistm.
I use BlackPill stm32f401ccu6 and I need to work with I2C bus PB6/PB7.
Earlier I wrote an issue about BlackPill hardware, because. possible damage to the PA10 port.
But as soon as I connect the serial port PA9/PA10 and the I2C bus, nothing works.
I'm starting to deal with serial ports.
The code is following

//                      RX    TX
HardwareSerial Serial3(PA10, PA9);
HardwareSerial Serial2(PB7, PB6);

void setup() {
  Serial3.begin(115200);
  Serial2.begin(115200);  
}

void loop() {
  Serial3.println("I am serial 3");
  Serial2.println("I am serial 2");
  delay(1000);
}

The code is just to check if serial ports are working.
This code was checked on 3 BlackPill and the work is equally wrong everywhere.
First, the code in the infinite loop is executed only 1 time.

In the screenshot below, each output is a separate press of the RESET button.
The output is single and without a line break, although the code indicates
println
When I connect CH340 to the PA9(TX) leg, I get the output
I am serial 3
When I connect CH340 to the PB6(TX) leg, I get exactly the same output
I am serial 3
And there is no line break.
What am I doing wrong?
PS.
If you specify Serial1, then the code does not compile at all ...
The compiler reports that the Serial1 variable has already been defined in the HardwareSerial.cpp.o file

c:/users/admin/appdata/local/arduino15/packages/stmicroelectronics/tools/xpack-arm-none-eabi-gcc/10.3.1-2.3/bin/../lib/gcc/arm-none-eabi/10.3.1/../../../../arm-none-eabi/bin/ld.exe: C:\Users\admin\AppData\Local\Temp\arduino_cache_876671\core\core_71ce6b1b0fb14fa3999cc585d1e98a16.a(HardwareSerial.cpp.o):(.bss.Serial1+0x0): multiple definition of `Serial1'; sketch\Test.ino.cpp.o:(.bss.Serial1+0x0): first defined here
collect2.exe: error: ld returned 1 exit status
exit status 1

Code doesn't work if I set define

HardwareSerial Serial2(PA10, PA9);
  #define SerialPort Serial2
void setup() {
  SerialPort .begin(115200);  
}

void loop() {
  SerialPort .println("I am serial 2");
}

During compilation error also.

[fpistm]

Answered here #2077