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Hello. Unfortunately, due to the age of that app, it just doesn't work well. And Panasonic hasn't bothered to update it for that TV, and if they haven't by now, they likely won't. This is an issue many people are reporting. It's one of the reason that I don't recommend Panasonic TVs when people ask me. They just don't keep their TVs updated which is an absolute necessity these days. There's really not anything you can do. As you already know, your network is likely solid. The issue isn't on Amazon's end. It's just that app on that TV.
The only way around it would be to get another device like a Fire Stick or a Roku. I personally prefer the Fire, but you can't go wrong with either one. Here's a link to purchase one online. https://amzn.to/2XgvYOe
And if you still wish to connect it wired, they do make an adapter. Here's the one I use: https://amzn.to/2IlUipO
I know it's not the answer you want to hear, but there's really nothing that can be done on the TV itself.
If that answers your question, please be sure to rate my answer 5 stars. Otherwise just let me know if you still need help with it.