The debug logs you provided above is from "Toolset Forms Commerce" plugin, please find and edit the post/user form with "Forms Commerce" settings, in section "Toolset Forms Commerce", option "Checkout process", choose "Clear the cart and include only the selected product"
1) In case it is a compatibility problem, please deactivate all other plugins, and switch to wordpress default theme 2020, deactivate all custom PHP snippets, and test again
2) If the problem still persists, please provide database dump file(ZIP file) of your website, you can put the package files in your own google drive disk, share the link only, also point out the problem page URL, how to trigger the PHP error debug logs in front-end or admin side, I need to test and debug it in my localhost, thanks https://toolset.com/faq/provide-supporters-copy-site/
I have a site setup for testing already, dev.teachingselfgovernment.com. I'll share the login info for an administrator account, just send me a new secure form.
I did disable all plugins except Elementor Pro, Error Log Monitor, WooCommerce, and Toolset. I only left WooCommerce on because WooCommerce Blocks requires it. I left Elementor on so the site looks normal, and the Error Log Monitor so I can easily monitor the logs.
I'm not sure what I would have to do to trigger that error again though.
Private message box enabled again, and if there are detail steps for "how to trigger the PHP error debug logs in front-end or admin side", that will be helpful, thanks
I have checked all post forms and user forms in your website, there isn't "Toolset Forms Commerce" setting in it, if you don't need it, you can deactivate "Toolset Forms Commerce" plugin.
And before you reinstall WooCommerce plugin, you can backup your website database first, all Toolset and Woocommerce setting should in your website database, it is safe to delete the plugin files.
