Hi Alex:
Have you posted all of the code for your site?
Also I noted this comment:
type mismatch of some kind? does it matter that this is a reference field and the key in the referenced collection is a different name of the key in the parent collection?
It may be worth exploring this further. You might need to go back to the table that is connected to $w(‘#dataset1’) and examine the field name and field key values. Normally when you create a column in a data collection you enter the field name and the Editor generates a key field based on the field name. So for example if you added a field called First Name then the editor generate a field key firstName . The field key is what you need to be using when accessing data collection properties in returned results.
Now here’s the thing. If you decide to rename the column by changing the field name the field key WILL NOT change. So in the example above if you decide you prefer to have Parent First Name as the new field name the field key will remain as firstName . So if the column you have set the field name as email to in the database was originally Email Address and you renamed it to email at some point then the field key would be emailAddress and not email .

If you are using the wrong key then you will get an error.
One other thing you can do is dump the dataset in the onready function like this to see what it is you think you are filtering:
$w('#dataset1').onReady(() => {
$w('#dataset1').getItems(0, $w('#dataset1').getTotalCount())
.then((results) => {
console.log('===============> Dumping dataset1 <===============');
console.log(results);
console.log('===============> End dump dataset1 <===============');
return wixUsers.currentUser.getEmail();
})
.then((email) => {
console.log(email, 'here is the email being sent to filter');
return $w("#dataset1").setFilter(wixData.filter()
.eq("email", email) );
})
.then( () => {
console.log("Dataset is now filtered");
})
.catch( (err) =>
console.log(err);
});
}
Then post the results if you can’t see any issues.
Other than that without seeing all of the page code (if this isn’t it all) or access to the page to examine in the browser console then helping you figure this out will be tough.
Cheers
Steve