Wipeout app uses Shopify's hiding feature which has the advantage of hiding sold-out products from collections as well as search results.

The downside is that Shopify also hides the product details page which is why you are seeing the 404 error.
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Due to this limitation, our app does not support SEO-friendly hiding. This is mentioned clearly in our FAQ and App Store listing
If you are concerned about SEO due to 404 errors, then our app is not a good fit for your needs.

​Next steps for you:

1. Uninstall our app from the Installed Apps page.

2. Then Publish back all the hidden out-of-stock products using the Shopify Products Admin. It is the easiest and fastest way to publish back all hidden products in your store.

3. Instead of using an app you can use Shopify's Automated Collections feature to show only in-stock products in your collections. This is SEO-friendly.