Preview not working for manual filled dropdown?

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Below is my code for loading my dropdown:

async function loadClassTypes() {
    const results = await $w('#classTypeDataset').getItems(0, 20);
    const options = [];
    for (let i = 0; i < results.items.length; i++) {
        const next = {
            label: results.items[i].classType,
            value: results.items[i]._id,
        }
        options.push(next);
    }
    $w('#classTypeDropDown').options = options;
    $w('#classTypeDropDown').selectedIndex = defaultClassTypeIndex;
}

When I Preview my form, the dropdown is empty:

When I Publish the form, the list loads just fine:

In Preview, if I log the contents of the dropdown, it shows the expected values:

This was all working in Preview until I tried it on the morning of 7/26/2021. Is this a new Velo bug with Preview or am I doing something wrong? Is anyone else having a similar issue?