Anything inside void loop if statement does not work...WHYYYY? about tinygpsplus

[JasonPittenger]

gps.encode() processes the data one byte at a time.
You really don't want to be testing the return for every byte.

The best bet is to separate the serial reading & gps encoding from everything else.
Also, don't use delay(10);
This stops all processing for 10 milliseconds.
Instead, use millis().
This will cause the loop to continue running, and reading the GPS data.
Then every 10 milliseconds, it will jump into the code that actually updates the LEDs.

Try this. (NOTE: I did not build or run this, so it might have errors. But it should be at least 95% correct)

loop()
{
	uint16_t GPSbytesAvailable;
	uint32_t LED_Update;
	uint8_t BlueCounter = 1;

	GPSbytesAvailable = GPS_Serial.available();
	while(GPSbytesAvailable--)
	{
		gps.encode(GPS_Serial.read());
	}
	
	if((millis() - LED_Update) >= 10))
	{
		LED_Update = millis();
		if (gps.speed.isValid()) 
		{
			BlueCounter = 1;
			age = gps.speed.age();
			Serial.print("Speed: ");
			Serial.print(gps.speed.mph());
			Serial.println(" mph");
	
			static uint8_t hue = 0; // Starting hue value
			static uint8_t wavePosition = 0; // Current position of the wave
	
			// Calculate color for each LED based on wave position
			for (int i = 0; i < NUM_LEDS; i++) 
			{
				uint8_t color = sin8(i * 8 + wavePosition); // Use sine function for color intensity
				leds[i] = CHSV(hue, 255, color); // Set color based on hue and intensity
			}
			wavePosition++; // Increment wave position for the next frame
		}
		else
		{
			Serial.println("No speed data");
	
			// Slowly pulses blue when "No speed data" is presented.
			uint8_t blue = 0; // Blue color value
			if(BlueCounter)
			{
				blue = sin8(BlueCounter);
				fill_solid(leds, NUM_LEDS, CRGB(0, 0, blue));
				BlueCounter++
			}
			else
			{
				// Set all LEDs to off
				fill_solid(leds, NUM_LEDS, CRGB(0, 0, 0)); // Off
			}
		}
		FastLED.show();
	}
}

[svdrummer]

If this is complete, please close it