When including SPIFF.h de compiler encounters an error:
undefined reference to vtable for fs::FileImpl
Same include in Arduino 2.x and Visual Code PlatformIO OK

Sample code:

#include <SPIFFS.h>

int myFunction(int, int);

int delayTime = 500;

void setup() {
  pinMode(2, OUTPUT);           // Green
  pinMode(0, OUTPUT);           // Red
  pinMode(4, OUTPUT);           // Blue
  Serial.begin(115200);
}

void loop() {
  digitalWrite( 2, HIGH);
  delay( delayTime );
  digitalWrite( 0, HIGH);
  delay( delayTime );
  digitalWrite( 4, HIGH);
  delay( delayTime );
  digitalWrite( 2, LOW);
  delay( delayTime );
  digitalWrite( 0, LOW);
  delay( delayTime );
  digitalWrite( 4, LOW);
  delay( delayTime );
  Serial.println("TSP - This is main.\n");
}

It is not a bug, you need to leave the optimization at the default level to compare with arduino 2 or platformio. Some cores and some libraries can not compile with optimization entirely disabled. 

You can either select a different optimization option or read about using #pragma to push and pop gcc optimization for certain code parts.