Laggy playback all of a sudden in UI

I typically save recordings in .mp4 playback so that it's easier for family remembers to view videos from computers on my network. Recently, I noticed that the UI3 playback (via the local LAN IP address), has been choppy or laggy. These pauses are not showing up on the files themselves which run perfect. Any idea other than network congestion that may cause these lags? I've tried both Firefox and Chrome. The server computer is hooked up via Ethernet to the router and speed tests out at around 900Mbps.