Puzzle with arduino uno Rev3 - Led is blinking only if serial.prin is used...

Hello everybody
I am currently develop the Arduino code for my dynamic simulator (see https://www.xsimulator.net/community/threads/launching-of-my-6dof-low-cost-dynamic-simulator.11594/ =Launching of my 6dof low cost dynamic simulator).
I am using the timer 2 (for several counters, ...) and I have the following problem, that can simply illustrate with a simple blinking led code:
1) In the first version, where I use print.serial to control the counter progress, the led is well blinking.
2) In the 2nd version, where I just suppress the line "print.serial(...), the led is stoppink to blink !!!!!! I do not understand, theoricaly there is not side effect with the function print.serial, no ?
Congratulation and thank you a lot if you find the raison, and the solution:

1) version with "print.serial" :

unsigned int counter_generic, toggle=0;
void setup() {
Serial.begin(115200);
pinMode(LED_BUILTIN, OUTPUT);
// timer 2 configured at 16uS (62500 Hz)
cli(); // Unactivation of the globale interruption
bitClear (TCCR2A, WGM20); // WGM20 = 0
bitClear (TCCR2A, WGM21); // WGM21 = 0
TCCR2B = 0b00000110; // Clock / 256 soit 16 uS et WGM22 = 0
TIMSK2 = 0b00000001; // Locale interruption autorised by TOIE0
sei(); // Activation of the globale interruption}
void loop() {
if (toggle == 0){
digitalWrite (LED_BUILTIN,1);
toggle = 1;}
else {
digitalWrite (LED_BUILTIN,0);
toggle = 0;}
// delay 1 seconds
counter_generic=0;
delay_1s_a:
if (counter_generic < 1000 ){
Serial.println(counter_generic);
goto delay_1s_a;}
}
// Routine d'interruption timer 2
ISR(TIMER2_OVF_vect)
{ TCNT2 = 256 - 62; // 62 x 16 µS = 0,992 µS, so close to 1mS
counter_generic++;}


2) version without "print.serial" (you can check, nothing else is changed) but the led do not want to blink...:


unsigned int counter_generic, toggle=0;
void setup(){
Serial.begin(115200);
pinMode(LED_BUILTIN, OUTPUT);

// timer 2 configured at 16uS (62500 Hz)
cli(); // Unactivation of the globale interruption
bitClear (TCCR2A, WGM20); // WGM20 = 0
bitClear (TCCR2A, WGM21); // WGM21 = 0
TCCR2B = 0b00000110; // Clock / 256 soit 16 uS et WGM22 = 0
TIMSK2 = 0b00000001; // Locale interruption autorised by TOIE0
sei();} // Activation of the globale interruption}
void loop(){
if ( toggle == 0){
digitalWrite (LED_BUILTIN,1);
toggle = 1;}
else {
digitalWrite (LED_BUILTIN,0);
toggle = 0;}
// delay 1 seconds
counter_generic=0;
delay_1s_a:
if (counter_generic < 1000 ){
// Serial.println(counter_generic);
goto delay_1s_a;}}
// Routine d'interruption timer 2
ISR(TIMER2_OVF_vect)
{ TCNT2 = 256 - 62; // 62 x 16 µS = 0,992 µS, so close to 1mS
counter_generic++;}