JSON Array looses content after loop iterations

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1

hello together,
I am really struggeling with json right now. I have a callback function in which a JSON array is beeing filled each time its executed. In a different function I print the serialized JSON document with the array. However, after about 7 iterations (depending on the siue of the array items, the print out becomes empty:

{"response":[{"profile_id":"1","profile_name":"vader"},{"profile_id":"2","profile_name":"luke"},{"profile_id":"3","profile_name":null}],"code":1}
this part obove is the correct content
Opened database successfully
Operation done successfully
Time taken:172 ms
{"response":[],"code":2}
this part obove is missing the array content
Opened database successfully
Operation done successfully
Time taken:170 ms
{"response":[],"code":0}
here is some extraction of my code:

String buffering;
StaticJsonDocument < 4096 > doc;
JsonArray daten = doc.createNestedArray("response"); 

//-----------------DB Enquery-----------------------
void db_enquery(String enquery) {
buffering="";
	doc["code"] = random(0,3);
 for(int i=daten.size();i>=0;--i)daten.remove(i);
	db_open();


	db_exec(enquery.c_str());
serializeJson(doc,Serial);
serializeJson(doc,buffering);
	if (db_file_name[0] != 0) {
		db_file_name[0] = 0;
		sqlite3_close(db);
	}

}
//-----------------DB Enquery-----------------------
//-----------------mein Callback for sql enqueries----------------------
static int callback(void * data, int argc, char * *argv, char * *azColName) {
	
  
  StaticJsonDocument<1800> docx;
  JsonObject sub = docx.createNestedObject();

  
	//Serial.println(String(counter));

	for (int i = 0; i < argc; i++) {

		sub[azColName[i]] = String(argv[i]);

	}
daten.add(sub);



	counter++;


return 0;
}
//-----------------mein Callback for sql enqueries----------------------
//-----------------open Database----------------------
int db_open() {
	if (db != NULL) sqlite3_close(db);
	int rc = sqlite3_open(DATABASE_NAME, &db);
	if (rc) {
		Serial.print(F("Can't open database: "));
		Serial.print(sqlite3_extended_errcode(db));
		Serial.print(" ");
		Serial.println(sqlite3_errmsg(db));
		return rc;
	} else Serial.println(F("Opened database successfully"));
	return rc;
}

char * zErrMsg = 0;
const char * data = "Output:";

int db_exec(const char * sql) {
	counter = 0;
	if (db == NULL) {
		Serial.println("No database open");
		return 0;
	}

	first_time = true;
	long start = micros();

	int rc = sqlite3_exec(db, sql, callback, (void * ) data, &zErrMsg);
//serializeJson(doc, Serial);
//Serial.println("\r\n");

	if (rc != SQLITE_OK) {
		Serial.print(F("SQL error: "));
		Serial.print(sqlite3_extended_errcode(db));
		Serial.print(" ");
		Serial.println(zErrMsg);
		sqlite3_free(zErrMsg);
	} else {
		Serial.println(F("Operation done successfully"));
	}

	Serial.print(F("Time taken:"));
	Serial.print((micros() - start) / 1000);
	Serial.println(F(" ms"));


	return rc;

}
2 
 for(int i=daten.size();i>=0;--i)daten.remove(i);

do you have really i+1 elements in your data ?

In your function when you declare docx as a StaticJsonDocument

static int callback(void * data, int argc, char * *argv, char * *azColName) 
{ 
  StaticJsonDocument<1800> docx;
  ...

your allocate the memory pool on the stack. 1800 can potentially be big for the stack, you could have a stack overflow. Have you tried switching to a DynamicJsonDocument?