Help: Internet is painfully slow on FireTv, fine on other Kodi device

I'm looking for some advice on a problem I've been having with Kodi on my Amazon FireTv for a while.

I'm running Krypton (17.1) on my FireTv and an Android Tablet (Samsung Galaxy Tab S2). Both are connected wirelessly to a router that speed tests at around 100mbps regularly from any device in my home.

When I try to watch anything within Kodi on the FireTv I get constant buffering and "The source is too slow for constant playback" message. I can pull up the exact same source on my tablet and watch with no buffering or messages.

What does that mean? Is there some setting I can check or some full folder I can clear out? Is my ISP targeting that device somehow? Will I need to get a VPN to see improved speed?

I appreciate any suggestions or feedback. Thanks!