Nice job. Packet loss will definitely cause these issues. Now, you just need to find the source of the packet loss.
In your situation, I’d first try to figure out if it is ISP/Internet before looking inside either network. I wouldn’t expect it to be internal at these speeds. Though, did you get CPU/RAM readings on the network equipment during these tests? Maxing out either can result in packet loss.
I’d start with two pairs of packet captures when the issue happened: endpoint to endpoint and edge router to edge router. Figure out if the packet loss is only happening in one direction or not. That is, are all the UK packets reaching DE but not all the DE making it back? You should clearly be able to narrow into a TCP conversation with dropped packets. Dropped packets aren’t ones that a system never sent, they’re ones that a system never received. Find some of those and start figuring out where the drop happened.
The person isn’t talking about automating being difficult for a hosted website. They’re talking about a third party system that doesn’t give you an easy way to automate, just a web gui for uploading a cert. For example, our WAP interface or our on-premise ERP don’t offer a way to automate. Sure, we could probably create code to automate it and run the risk it breaks after a vendor update. It’s easier to pay for a 12 month cert and do it manually.