Use a wired baseline
If the same stream stutters on Wi-Fi, connect by Ethernet and verify the active network. Run the same ten-minute sample. Note dropped frames, quality changes or stalls separately. If the result is stable on both links but one specific source stutters, inspect the source format in the player.
Include the display chain
Record the HDMI display and any receiver, the current output mode and whether the fault occurs when audio or picture format changes. Compare one lower-quality variant if the source offers it. Give support the stream's format and device model, not the account URL.