Magento 2.2.6: Scheduled catalog_product_alert cron jobs failing with NotLoadInfoImageException: Can't get information about picture:

Question

I'm currently experiencing an issue where my scheduled catalog_product_alert cron jobs in the cron_schedule table are all failing to send a back-in-stock product alert. Each time these are executed, the following exception is thrown and the product alert email is never sent out while also setting the alert as having been sent in the product_alert_stock table.

[2019-03-26 00:45:03] main.CRITICAL: Can't get information about the picture:  {"exception":"[object] (Magento\\Catalog\\Model\\Product\\Image\\NotLoadInfoImageException(code: 0): Can't get information about the picture:  at /home/xxx/public_html/yyy/vendor/magento/module-catalog/Model/Product/Image.php:834, TypeError(code: 0): Argument 1 passed to Magento\\Catalog\\Model\\Product\\Image::loadImageInfoFromCache() must be of the type string, null given, called in /home/xxx/public_html/yyy/vendor/magento/module-catalog/Model/Product/Image.php on line 880 at /home/xxx/public_html/yyy/vendor/magento/module-catalog/Model/Product/Image.php:913)"} []

Does anyone know any possible reasons that I might be running into this issue? All of the products that I have been testing the back-in-stock alert with have images (base, small, thumbnail) so I don't know what could possibly be causing this issue.

I am currently using Magento ver 2.2.6

Any and all help would be really appreciated!