Mongoose using $push on an array field overwrites last entry - node.js

Question

I am trying to create an eventlog type of field on mongodb records where I can store a list of activity. The first time I run the function, it appends to the array correctly but subsequent calls overwrite the last entry instead of appending. If I restart the server or refresh the page in the browser, it will append once again then repeat the same behavior.
I'm learning node and javascript so I'm sure it's some mistake I've made but I don't seem able to figure it out.
Javascript on the client is a tabulator event.
cellEdited:function(cell){
//cell - cell component
const oldValue = cell.cell.oldValue;
const newValue = cell.cell.value;
const title = cell.cell.column.definition.title;
var report = cell.cell.row.data;
report.event = `Updated ${title} from ${oldValue} to ${newValue}`;
$.ajax({
type: 'POST',
url: '/api/update',
data: report,
dataType: 'json'
});
}
The route that its calling on the server:
app.post('/api/update', isAuthenticated, function(req, res) {
var report = req.body;
var reason = '';
if (typeof report.event !== 'undefined') {
reason = report.event;
delete report.event;
} else {
reason = 'Report updated';
}
db.DamageReport.findOneAndUpdate({ _id: report._id}, report, function (err, doc) {
if (err) {
console.log('Err updating report ', err);
return res.send(500, { error: err});
}
/*
* Write eventlog
*/
var event = {"date": new Date(), "user": req.user.email, "event": reason };
appendLog(doc._id, event);
return res.json(doc);
});
});
The appendLog function:
function appendLog(id, entry) {
/*
* entry format:
* date: Date
* user: String
* event: String
*/
if (typeof(entry.date) !== 'object') {
entry.date = new Date();
}
db.DamageReport.findByIdAndUpdate(id, {$push: {eventLog: entry}}, function(err, result) {
if (err) {
return console.log('Error writing eventLog: ', err);
}
return(result);
});
}

Answer 1

It wouldn't append more than one because the previous save contained the Eventlog array in it's original form so every time it saved, it set it back to the original array and then appended the last update.