Arduino RTC subtracting 1 second every 8 hours - c++

Question

I used the RTC, from an Arduino MKR 1300 with integrated RTC, as an alarm that will trigger a "boolean"(it's an integer) that will tell the loop to run a certain method every minute and then send some data every 5 minutes. It's on an active loop but the method to send data ONLY WORKS if it's inside the loop (no idea why). The problem is the RTC apparently is subtracting 1 second at every 8 hours or so after a few days the timing might come off and instead of sending data every xx:10:xx-xx:15:xx it might send data xx:09:xx-xx:14:xx.
Here's the code:
#include <EmonLib.h>
#include <RTCZero.h>
#include <MKRWAN.h>
EnergyMonitor emon1;
EnergyMonitor emon2;
EnergyMonitor emon3;
RTCZero rtc;
LoRaModem modem;
String appEui = "1234567891011121";
String appKey = "ffffffffffffffffffffffffffffffff";
/* INITIAL_TIME */
const byte seconds = 0;
const byte minutes = 0;
const byte hours = 0;
const byte day = 17;
const byte month = 12;
const byte year = 18;
byte second_alarm = 0;
byte minute_alarm = 0;
byte hour_alarm = 0;
byte INTERVAL = 60;
int SEND_LOOP = 5;
int totalKW;
int counter= 0;
int alarm_Triggered = 0;
void setup()
{
Serial.begin(115200);
if (!modem.begin(EU868)) {
Serial.println("Failed to start module");
while (1) {}
};
Serial.print("Your module version is: ");
Serial.println(modem.version());
Serial.print("Your device EUI is: ");
Serial.println(modem.deviceEUI());
Serial.println("Connecting");
int connected = modem.joinOTAA(appEui, appKey);
if (!connected) {
Serial.println("Something went wrong; are you indoor? Move near a window and retry");
while (1) {}
}
Serial.println("Connected");
// Set poll interval to 60 secs.
modem.minPollInterval(60);
analogReadResolution(9);
emon1.current(1, 53);
emon2.current(2, 53);
emon3.current(3, 53);
counter= 0;
rtc.begin(); // initialize RTC
rtc.setAlarmTime(hour_alarm, minute_alarm, second_alarm);
rtc.enableAlarm(rtc.MATCH_HHMMSS);
rtc.attachInterrupt(triggerAlarm);
// Set the time
rtc.setHours(hours);
rtc.setMinutes(minutes);
rtc.setSeconds(seconds);
// Set the date
rtc.setDay(day);
rtc.setMonth(month);
rtc.setYear(year);
}
void loop() {
if (alarm_Triggered == 1) {
dataMonitor();
alarm_Triggered = 0;
}
}
void dataMonitor() {
int totalWatt = 0;
unsigned long delay_send = 0;
int sending = 0;
double Irms1 = emon1.calcIrms(600);
if (Irms1 < 0.3) Irms1 = 0;
double Watt1 = Irms1 * 230;
double Irms2 = emon2.calcIrms(600);
if (Irms2 < 0.3) Irms2 = 0;
double Watt2 = Irms2 * 230;
double Irms3 = emon3.calcIrms(600);
if (Irms3 < 0.3) Irms3 = 0;
double Watt3 = Irms3 * 230;
totalWatt = Watt1 + Watt2 + Watt3;
totalKW = totalKW + totalWatt / 1000;
Serial.println(counter);
sendDataChecker(Irms1, Irms2, Irms3);
setAlarm();
counter= counter+ 1;
}
void sendDataChecker(double Irms1, double Irms2, double Irms3) {
if (counter== SEND_LOOP) {
double IrmsTotal = Irms1 + Irms2 + Irms3;
String msg = "{\"id\":\"avac_aud2\",\"kW\":" + String(totalKW) + ", \"current\":" + String(IrmsTotal) + "}";
int err;
Serial.println("Ready to Send");
modem.beginPacket();
modem.print(msg);
err = modem.endPacket(true);
Serial.println("Sent1");
if (err > 0) {
//message sent correctly
Serial.println("Sent");
counter= 0;
totalKW = 0;
} else {
Serial.println("ERR");
counter= 0;
}
}
}
void setAlarm() {
second_alarm += INTERVAL;
if (second_alarm >= 60) {
minute_alarm++;
second_alarm = 0;
}
if (minute_alarm >= 60) {
hour_alarm++;
minute_alarm = 0;
}
if (hour_alarm >= 24) {
hour_alarm = 0;
}
rtc.setAlarmTime(hour_alarm, minute_alarm, second_alarm);
}
void triggerAlarm() {
alarm_Triggered = 1;
}