Thank you Felix for the quick answer. I confess did not looked in the M5 source. So its more a feature than a bug.
My problem was, that i am communicating with other hardware where i can not easily change the baudrate to 115200. Must touch the M5Stack lib for that.
A property for baudrate value would be nice.
Still do not understand why the problem was only since the esp32 release to 1.0.5 and not earlier.
Regards Patrick

Hello,
I would like to report an issue with M5Stack Core GRAY/BASIC.
If you have installed esp32 board lib v1.0.5 and run code like above, you will find that the statement Serial.begin() has a conflict with the statement M5.begin(). You will never get into the loop.
With esp32 1.0.4 and lower it is ok.
The strange thing is that when i remove Serial.begin() it works and still prints with 115200 baud.
I do not know wether the issue is in the lib esp32 or m5stack.
Regards Patrick

Here is an example:
/******************************************************************************/
#include <M5Stack.h>

int i = 0;

void setup(void) {
Serial.begin(115200); // comment this line if esp32 lib 1.0.5 is installed!

M5.begin();
M5.Power.begin();
M5.Lcd.setCursor(10, 20, 4);
M5.Lcd.setTextColor(TFT_YELLOW);
M5.Lcd.setTextSize(1);
M5.Lcd.print("Hello World!");
delay(2000);
M5.Lcd.clear(TFT_BLACK);
}

void loop() {
M5.Lcd.setCursor(10, 20, 4);
M5.Lcd.fillRect(10, 20, 100, 19, TFT_BLACK);
M5.Lcd.println(i);

Serial.println(i);
i++;
delay(1000);
}
/******************************************************************************/

Find the bug:
"for(int i=0; i>=100; i++) {"
in ... https://github.com/m5stack/M5Stack/blob/master/examples/Basics/FactoryTest/FactoryTest.ino

How do i print these characters to LCD? I own the M5stack Grey.
With other Arduino LCD's i did "\xEF" to print 'ö'. But with M5 LCD it did not work.
Is there a document showing wich characters are supported in the LCD font?
Patrick