Hi,
I was having weird checkout issues during the last week and through "trial and error" (disabling all plugins and re-enabling them one by one) I could identify the ATUM Product Level plugin as the culprit:
Here one video (https://youtu.be/wVfd2znQozM) showing the checkout process with the plugin enabled (ending in an internal server error) and here a second video (https://youtu.be/wVfd2znQozM) showing the same checkout process with the plugin disabled (checkout working fine).
Here the wp-debug.log entry for the 500 Internal server error causing the issue:
[13-Jun-2021 19:41:46 UTC] PHP Fatal error: Uncaught Error: Object of class WC_Data_Store could not be converted to string in /var/www/onetwo3d/staging-site/wp-content/plugins/atum-stock-manager-for-woocommerce/classes/Components/AtumCache.php:62
Stack trace:
#0 [internal function]: Atum\Components\AtumCache::Atum\Components{closure}(Object(WC_Data_Store), '\x00*\x00data_store')
#1 /var/www/onetwo3d/staging-site/wp-content/plugins/atum-stock-manager-for-woocommerce/classes/Components/AtumCache.php(63): array_walk_recursive(Array, Object(Closure))
#2 /var/www/onetwo3d/staging-site/wp-content/plugins/atum-product-levels/classes/Models/BOMModel.php(107): Atum\Components\AtumCache::get_cache_key('has_linked_bom', Array)
#3 /var/www/onetwo3d/staging-site/wp-content/plugins/atum-product-levels/classes/Inc/Hooks.php(3297): AtumLevels\Models\BOMModel::has_linked_bom(Object(WC_Product_Woosb))
#4 /var/www/onetwo3d/staging-site/wp-content/plugins/atum-product-levels/classes/Inc/Hooks.php(3284): AtumLevels\Inc\Hooks->maybe_prevent_sending_stock_emails('woocommerc in /var/www/onetwo3d/staging-site/wp-content/plugins/atum-stock-manager-for-woocommerce/classes/Components/AtumCache.php on line 62
Can you please try to fix this as soon as possible, as it is causing me quite a lot of trouble in the shop. Customers are sending their orders several times, as they always getting kicked back to the checkout page instead of the order confirmation page (but in the background the order is still being processed), which is leading to high cost in payment refunds.