Warning, there's a long reply to your long reply. :)
Took the time to read through, thanks again for the details. I made an image for you to give you a better idea of my setup and where things are positioned in the current setup. This is only 2 points. The router, and an additional router on the 3rd floor. This is our current setup. I've checked my speed at different places throughout the house and added that to the image as well. I'm seeing a little better on the downloads. My wife reported a complete internet drop about two hours ago, but I did not have the same drop in my office. Before she told me that I was getting 620 up and down in my office on the wired. Since then it's like 600 down 50 up. (Router still shows 550 up though) Here's the diagram:
Something is up, this was fine for a long time. I found a thread on the google support forums basically stating there's a firmware update causing problems for a lot of people. I ordered the UI Dream Router and two points. My job deals with software so my company sent me a pack they had as well of some TP-Link.
Here's a link for the ui and another for the TP-Link ones they are sending me. I will have a weekend project on my hands for sure. I can decided which one I want to use. The TP-Link isn't looking like a bad option with 3 floors and a cat6 connection on each floor.
TP-Link Deco 3 Pack -
https://www.amazon.com/gp/product/B085Z35GY6/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
Ubiquiti UniFi Dream Router
I need to make it through tonight and tomorrow with the Google Wifi still though so I may reset all to factory tonight and switch the 3rd floor router to be the main router and the main router in the garage now to be the 3rd/2nd floor access point just to see if it helps.
I understand some will look at my post and say "well they just switched after asking for help once". I assure you, that's not the case. This was my last stop before ripping these things out. I have around $500-$600 invested in Google Wifi and really tried to get it worked. I put in days of work to finish the cat 6 runs in my house and take as much of the load off the wifi as possible and build a nice stable wired network. I have moved points, reset points, bought power cords, removed special characters from wifi passwords, identified every item on the network, checked every single cat6 in the house with a network tester.
All of this to say "I tried". After a year of use, I'm just not happy with the Google Wifi product. It's not good. I've had to put in much more work, troubleshooting, and time than you should for a product that cost this much and advertises how easy they are to setup and use.
IT Guy here. You have a wifi problem. I have a very nice WiFi router myself... Asus RT-AX86U and even it will make stupid channel choices if left in auto mode. If I force the 2.4GHz and 5Ghz radios onto the right channels, it has amazing range and speed.
You probably need a better and well configured Wifi router. You also need to do some speed tests throughout the day/week to ensure that your internet provider is actually serving you the 500 mbps that they are charging you for. For people that don't like to fiddle with routers, I usually recommend replacing the whole system with a two or three node mesh network. TP-Link makes a pretty decent one that won't break the bank.
If you just want to solve this FireStick/YTTV buffering problem then the cheapest thing to do is run an ethernet cable to your firestick. Honestly, spending a little money to have your expensive internet connection cover your entire house properly is worth the time and effort but I understand most people don't get as focused and picky about that as I do.
Okay. Thanks for the explanation.
Is "TP-LINK DECO WiFi 6/6E" this one? https://www.amazon.com/Mesh-Wifi-6-Router-System/dp/B085Z35GY6