Here is a demo-code that demonstrates it
// start of macros dbg and dbgi
#define dbg(myFixedText, variableName)
Serial.print( F(#myFixedText " " #variableName"=") );
Serial.println(variableName);
// usage: dbg("1:my fixed text",myVariable);
// myVariable can be any variable or expression that is defined in scope

#define dbgi(myFixedText, variableName,timeInterval)
do {
static unsigned long intervalStartTime;
if ( millis() - intervalStartTime >= timeInterval ){
intervalStartTime = millis();
Serial.print( F(#myFixedText " " #variableName"=") );
Serial.println(variableName);
}
} while (false);
// usage: dbgi("2:my fixed text",myVariable,1000);
// myVariable can be any variable or expression that is defined in scope
// third parameter is the time in milliseconds that must pass by until the next time a
// Serial.print is executed
// end of macros dbg and dbgi

#include <Button.h>
#include <Stepper.h>

#define LOOP_STATE_STOPPED 0
#define LOOP_STATE_STARTED 1

#define STEPS 2038 // (28BYJ-48)

Stepper stepper(STEPS, 8, 10, 9, 11);

const int myButton_pin = 7;

Button myButton(myButton_pin); // pin 7;
int loopState = LOOP_STATE_STOPPED;

void setup() {
Serial.begin(115200);
Serial.println( F("Setup-Start") );

myButton.setDebounceTime(50); // set debounce time to 50 milliseconds
}

void loop() {

myButton.loop();

if (myButton.isPressed()) {
dbgi("myButton.isPressed() is TRUE!",loopState,1000);
if (loopState == LOOP_STATE_STOPPED) {
loopState = LOOP_STATE_STARTED;
dbg("loopState = LOOP_STATE_STARTED",loopState);
}
else { // if(loopState == LOOP_STATE_STARTED)
loopState = LOOP_STATE_STOPPED;
dbg("loopState = LOOP_STATE_STOPPED",loopState);
}
}

if (loopState == LOOP_STATE_STARTED) {
dbg("if (loopState == LOOP_STATE_STARTED) delay(1000)...",loopState);

delay(1000);
stepper.setSpeed(400);             // 8 rpm
stepper.step(1019);              // 1019 steps half (for testing)
loopState = LOOP_STATE_STOPPED;  //stop ste
dbg("if (loopState == LOOP_STATE_STARTED) loopState = LOOP_STATE_STOPPED",loopState);

digitalWrite(8, LOW);  //turn off stepper hold to reduce power usage.
digitalWrite(9, LOW);
digitalWrite(10, LOW);
digitalWrite(11, LOW);
dbg("end of if (loopState == LOOP_STATE_STARTED",loopState); 

}
dbgi("End of loop/n/n",loopState,1000);
}

What the heck is causing this??