Parse.Query unable to find objects when called within Parse.Cloud code

I'm struggling to figure out why my queries will not work when called from Parse.Cloud triggers.

I want to define some logic after an object of particular class was saved (the class is 'Message' in my case).

I'm testing the following simple code in my cloud/main.js:

const conversationQuery = new Parse.Query('Conversation');
conversationQuery.get('myIdHere', { useMasterKey: true })
    .then(conversation => {
        console.log('### Conversation is', conversation);
    })
    .catch(err => {
        console.log('### Error is', err);
    });

Parse.Cloud.afterSave('Message', req => {
    const conversationQuery1 = new Parse.Query('Conversation');

    conversationQuery1.get('myIdHere', { useMasterKey: true })
    .then(conversation => {
        console.log('>>> Conversation is', conversation);
    })
    .catch(err => {
        console.log('>>> Error is', err);
    });
});

And when I start my instance of parse-server, the following is logged to the console:

### Conversation is { myObjectHere }

However, when I save any object of 'Message' class, I get an error:

>>> Error is { Error: Object not found. <stacktrace here>, message: 'Object not found.', code: 101 }

I'd expect it to log the very same object that was retreived when the server started but instead, it returns a '101 object not found' error.

I think I configured everything according to the documentation but there's a possibility I just missed something.

I'm using Parse Server 3.1.3 and Parse JS SDK 2.1.0