New products failing to validate

[hannahwoodward]

Description

Currently working on a site (with Craft multi-site enabled) where I've just switched off the 'multiple variants' setting for a product type, and now no new products can be created as they're failing to validate. The Craft flash notice says 'Couldn't save product.', then looking in the logs I find this:

2020-04-06 13:56:58 [-][1][6m88d4sbpo7e5a9l2pjukdkdmd][info][craft\services\Elements::_saveElementInternal] Element not saved due to validation error: Array
(
    [variants] => Array
        (
            [0] => Error saving variants
        )

)

Other notes:

• New products do save if I mark them as disabled, but I can't ever enable them
• Existing products can still be updated & are successfully saved without any issues
• I tried creating a new product type with exactly the same fields and without multiple variants. Creating a new product under this product type successfully saved.

Steps to reproduce

1. Create a product type with multiple variants enabled
2. Disable multiple variants
3. Try to create a new product

Additional info

• Craft version: 3.4.13
• PHP version: 7.4
• Database driver & version: MySQL 5.7.29
• Plugins & versions: Algolia (2.0.0), Amazon S3 (1.2.7), Asset Rev (6.0.2), Control Panel CSS (2.2.1), Craft Commerce (3.1.1), Events (1.4.4), Freeform (3.6.5), Icon Picker (1.1.2), Redactor (2.6.1), SEOmatic (3.2.50), Site Switcher (2.1.0), Stripe for Commerce (2.2.3), Super Table (2.4.7), Scout (2.2.2), Sentry SDK (1.0.6)

[lukeholder]

Could you send your database dump/backup to support@craftcms.com and reference this issue. We can then take a better look.

Also include the name of the product type etc.

[lukeholder]

Thanks @hannahwoodward I think we figured this out and have fixed it for the next release.