Would it be possible to try just a temporary Ethernet cable to see it that may work? I know you said you couldn’t move the router but maybe a long cable to test with?
Did you run a full speed test in Infuse with each change from Auto to 2 to Legacy?
Another possibility would be to try using FTP. Some users seem to have better luck with FTP over SMB.
There are so many variables with WiFi that it’s impossible to say what “normal” is. Many users have no issues what so ever with WiFi and others have constant problems.
The router, the distance, the brand of wireless, walls, what the dog ate for dinner, etc. all can change WiFi results. Even moving furniture in adjacent rooms can vary results.
You may be able to move the router up or down a foot or two and make a world of difference or check which band 2.4 GHz or 5GHz you’re using and maybe try the other.
Types of files also may be problematic, such as x265 for older ATVs and what codecs they use.
What model of ATV (I assume that’s what you’re using) or iOS device are you using?
I tried Ethernet and I get 400 Mbps, no buffering. Quality seems a bit better, also.
I tried connect the Apple TV to my mini (used to download the files) via Ethernet and it worked, too. However, I lose all internet functionalities on the Apple TV (Photos, Netflix etc)
It seems the Apple TV can’t manage both Ethernet and wifi at the same time.
I have confirmation from Apple that we can’t use both. I rearranged my setup and will unplug the Ethernet cable manually when needed. Problem solved.