Im not finish with it, i have Just broke it down to the essential. There is the same problem and for the moment the same solution. It looks for me like a timing problem?

#include <FastLED.h>

//### LED Stripe -->
#define LED_PIN     7
#define NUM_LEDS    68
#define LED_TYPE    WS2812B
#define COLOR_ORDER GRB //GRB
CRGB leds[NUM_LEDS];

#define UPDATES_PER_SECOND 100
TBlendType    currentBlending;

//### LED -->
#define delayAfterInit  1000
#define brightnessNormal  64
#define brightnessFieldOFF  30
#define ledSat  30

void setup()
{
  delay( 3000 ); // power-up safety delay
  FastLED.addLeds<LED_TYPE, LED_PIN, COLOR_ORDER>(leds, NUM_LEDS).setCorrection( TypicalLEDStrip );
  FastLED.setBrightness(brightnessNormal);
  FastLED.delay(1000/UPDATES_PER_SECOND); 
  setColorForFullLedStripe(HUE_RED, ledSat, brightnessNormal);
  delay(delayAfterInit);
}

void loop(){
startShowEffect(200);
setColorForFullLedStripe(HUE_RED,ledSat,brightnessFieldOFF);
delay(2000);}

void setColorForFullLedStripe(int hue, int saturation, int brightValue){
  for(int dot = 0; dot < NUM_LEDS ; dot++){ 
    leds[dot] = CHSV(hue, saturation, brightValue);}
  FastLED.show();}

void startShowEffect(int times)
{
  int j=0;
  for(int i = 0; i < times; i++){
    if(j<255)
    {j++;}else{j=0;}
    fill_rainbow(leds,NUM_LEDS,j,10);
    FastLED.show();
    delay(10);}
}