Nop 4.5.1: "PayPal Smart Payment Buttons" not on the site, but getting Bad Request error due to PayPal still sending request using its webhook

I have recently upgraded a site from 4.3 to 4.5.1. In the old site, PayPal Smart Buttons was being used. In the new site, PayPal Commerce is being used instead. There is nothing on the site or the application files related to the PayPal Smart Buttons plugin now. I have configured everything on the PayPal Commerce plugin and the PayPal account, and the live transactions are working properly. However, I'm getting these two errors frequently in the log:

1. Error 400. Bad request
2. Error 404. The requested page (/Plugins/PayPalSmartPaymentButtons/Webhook) was not found

They pop up whenever a payment is made, and sometimes just randomly. The requests are coming from PayPal's IP. Not sure what's going on.

Things I have done till now:
1. Removed all settings related to the PayPal Smart Buttons on the website/database
2. On the PayPal developer portal, removed the configurations that were set up for this plugin
3. Configured everything from scratch from both the nopCommerce website and the PayPal portal for the PayPal Commerce plugin.

I'm attaching the detailed error logs and the IP information from where the request was made. Please help me out with any ideas you've got. Thanks.

Error Logs:
1. https://www.screencast.com/t/KihHPvhVllNr
2. https://www.screencast.com/t/6jvzEjeL

IP: https://www.screencast.com/t/s9CQr1LKss

Perhaps when uninstalling PayPalSmartPaymentButtons plugin its webhooks were not deleted correctly. Go to PayPal developer portal → My apps & credentials → your live App, check the webhook list here, and just delete the ones you don't need.

I did that, was still getting the error. Then removed the app from the PayPal's dashboard, then did all the configurations from scratch, including adding the webhook for PayPal Commerce. It's the only webhook there now. The error is still here :(  

See the logs - https://www.screencast.com/t/Q6yBOqNK

Well, it's definitely somewhere on PayPal side, webhook hasn't been removed, and still posts requests every time configured event occurs.

Try to contact their support with your credentials, perhaps they will point you to which application this webhook.

Alternatively, if all the functions of current PayPal Commerce work fine, you can add a handler for this URL (/Plugins/PayPalSmartPaymentButtons/Webhook) to the plugin that returns Ok for all such requests, or even close this URL at the server level.