Express & MongoDB: Duplicate documents created at the timestamp - node.js

Question

I am using express with MongoDB as a database and while I am sending requests using Axios library to my backend, I have found that two documents were created at the time. I figured that out by checking the createdAt field and found the two documents have the exact timestamp. I am creating createdAt & updatedAt fields using mongoose-timestamp2
Here is the code responsible for sending the documents which have isSynchronized flag set to false
const syncExams = async (token) => {
let examSyncError;
await Exam.find({ isSynchronized: false })
.cursor()
.eachAsync(async (exam) => {
// use try/catch inside the loop
// so if problem occured in one document, others will be posted normally
try {
const formData = new FormData();
formData.append("exam", JSON.stringify(exam));
Object.keys(exam.images.toJSON()).forEach((key) => {
formData.append("images", fs.createReadStream(exam.images[key]));
});
const res = await axios.post(`${BACKEND_URL}/exams/`, formData, {
maxContentLength: Infinity,
maxBodyLength: Infinity,
headers: {
...formData.getHeaders(),
Authorization: `Bearer ${token}`,
},
});
console.log(res);
exam.isSynchronized = true;
await exam.save();
} catch (err) {
examSyncError = err;
}
});
if (examSyncError) {
throw examSyncError;
}
};
And here is the controller responsible for handling the coming request and creating these documents in the database.
router.post(
"/exams",
fileUpload.array("images"),
trimmer,
syncControllers.postExam
);
const postExam = async (req, res, next) => {
let createdExam;
let exam;
let patient;
try {
const reqBody = JSON.parse(req.body.exam);
reqBody.operator = reqBody.creator;
delete reqBody._id;
delete reqBody.creator;
const { nationalID } = reqBody;
patient = await Patient.findOne({
"personalData.nationalID": nationalID,
}).exec();
if (!patient) {
return next(errorEmitter("exams.get-patient.not-found", 404));
}
createdExam = new Exam(reqBody);
// insert the new paths of the images
Object.keys(reqBody.images).forEach((key, index) => {
createdExam.images[key.replace("Path", "")].Path = req.files[index].path
.split(path.sep)
.slice(-3)
.join(path.sep);
});
createdExam.patient = patient._id;
const checkDate = new Date(createdExam.examDate);
checkDate.setMonth(checkDate.getMonth() - 3);
const nearExam = await Exam.findOne({
patient: createdExam.patient,
examDate: { $gte: checkDate, $lt: createdExam.examDate },
isGradable: true,
});
if (nearExam) {
createdExam.isGradable = false;
}
exam = await createdExam.save();
patient.exams.push(createdExam);
await patient.save();
} catch (err) {
return next(errorEmitter("exams.create.fail", 500));
}
return res.status(201).json(exam.toObject({ getters: true }));
};
I am using the following package for createdAt & updatedAt records created using this plugin.
const timestamps = require("mongoose-timestamp2");
examSchema.plugin(timestamps);
This problem occurred in two or three cases only and did not happen again until then and I could not replicate the error. I do not what caused this!
What could cause this problem to occur? Is it possible that Axios sent the same request multiple times and mongoose created two documents at the same exact time, or it could be a bug in mongoose-timestamp2 plugin?
Any help would be appreciated, thank you!