We put a new smart TV in a studio built onto the back of our garage separate from our house. The old TV was not smart and required a Roku streaming stick. I'm guessing the new TV is close to 100 feet from the router and modem. We use a Linksys EA7500 Max-Stream AC1900 modem (5 GHz and 2.4 GHz bands). The old TV (LG) had decent reception with the streaming stick, but the new smart TV (Samsung) is not good. I moved the modem and router (Motorola) about six feet closer, and Amazon Prime seems to come in fine, but Netflix is constantly buffering.
I had to rearrange my practice room inside to move the modem, and the best way to do it ended up with the speakers in my bass amp, a Carvin MB210, placed about two feet away from the modem, and just below and to the right of a direct signal path to the Samsung. BTW, there is a refrigerator in the garage directly on the other side of the wall from the Samsung.
So (sorry, I can't quite tell from your description) the refrigerator (a.k.a large metallic radio-opaque object) is directly in the signal path?
Diagnostic one - still got the Roku stick? Does it work in the new TV same as it did in the old? My personal experience with Smart TV's is that they are Dumb as <word that will not be said as we are family-friendly here> and I've had MUCH better luck with a smart Blu-Ray player connected to a TV as if the TV was Dumb as... [the TVs never work well, and then they are quickly abandoned in terms of firmware upgrades. Blu-Rays seem to be supported for a much longer time with updated firmware.]
Diagnostic two - can you raise the (modem or router) on a cardboard box or the like temporarily?
Also - are you using (in close proximity to each other)
both a "Modem with built-in WiFi" (Linksys - that will also have a router and a switch, most likely) AND a "router" (which I presume in normal consumer speak is also a "router, switch, and wifi access point in one box" - Motorola?) That can cause problems with interference - much better is you run wire to separate them widely, each closer to one set of clients.
100 feet with walls in the way is a long shot - our mantra is that good WiFi is built on wires and fibers (and a "lousy" 100 meg ethernet cable will beat most wifi (it's actually 200 Mbit as it's bi-directional at the same time, and unlike WiFi there's virtually no overhead traffic) - a gigabit cable will utterly trounce "AC1900" (again it's bi-directional so equivalent to "2000" in WiFi speak, and does not have WiFi overhead.) For decent 5GHz reception, you should be able to see the access point from the receiver - not through a modern energy-efficient (radio mirror) window. 5GHz does not penetrate walls well, and if they happen to have foil-faced insulation, fuggedaboutit.
For loads like a TV (or a blu-ray player that's actually smart, attached to a TV) - (fixed location, wants lots of bandwidth) running a cable is really the best thing you can do. WiFi is great for laptops & tablets that move around a lot, and keeping your phone from burning 4G data. Cables beat them at moving data, and keeping the airwaves clear for the mobile-only devices.
[In the biz we apeak of Access Points (things that provide WiFi) Routers (things that do network creation, etc) and Modems (things that translate network from phone, cable TV, Fiber, Satellite, 4G, etc.) separately, and tend to run screaming from the consumer-oriented product that's all in one box doing all three.] Sanity is aided by having one modem unless you have redundant network suppliers and need two, one router unless you have serious uptime needs and require failover, and a bunch of access points, distributed widely and with power levels and channels selected to not interfere with each other, or at least not much.