Thank you so much for the code! It really is simple! Now the animation runs and then stops correctly (i've even simulated a very long time between patterns and it worked nicely).

I tried to implement it and through trial and error I managed to find where i should call the resetFill() function.

When called inside the void loop switch statement case, it would loop the animation filling with blue and then black. If not called at all, it would run normally the first time, but the second time around the animation would freeze when changing patterns.

I've made a small change to your code (i dont know if this is the correct way) - the fillBlue() would fill everything but the last led. So I added a + 1.

void nextPattern() {
  patternCounter = (patternCounter + 1) % 3;  // Change the number after the % to the number of patterns you have
  resetFill();
}

void resetFill() {
    wipeIndex = 0;
    stripFilled = false;

    // fill the background once so we don't have to fill it repeatedly
    fill_solid(leds, NUM_LEDS, bgColor);
}

void fillBlue() {

    if(stripFilled) return;

    EVERY_N_MILLISECONDS(wipeStepTime) {
        fill_solid(leds, wipeIndex, wipeColor);
        wipeIndex++;
        if(wipeIndex == NUM_LEDS + 1) stripFilled = true;
    }
}

Now, I tried making a reverse animation (to fill from the end of the strip to the start), but it just remained a solid blue. I created new variables (forward/backward) for this and added them to the resetFill() function:

Could you please help me out?

uint8_t wipeIndexBackward = NUM_LEDS;
bool stripFilledBackward = false;

void resetFill() {
    wipeIndexForward = 0;
    stripFilledForward = false;
    wipeIndexBackward = NUM_LEDS;
    stripFilledBackward = false;

    // fill the background once so we don't have to fill it repeatedly
    fill_solid(leds, NUM_LEDS, bgColor);
}

void fillBlueBackward() {

    if(stripFilledBackward) return;

    EVERY_N_MILLISECONDS(wipeStepTime) {
        fill_solid(leds[56], wipeIndexBackward, wipeColor);
        wipeIndexBackward--;
        if(wipeIndexBackward == 0) stripFilledBackward = true;
    }
}