The Funimation PS4 app uses a technology called "adaptative bitrate player." It keeps adjusting video quality as it goes along. The first four or five minutes of your session determine the video quality you will have for the rest of your session. So, suppose your environmental conditions vary noticeably after those first few minutes (your WiFi signal deteriorates, for example). In that case, the app won't work very well because it expects a video quality it can't have anymore. The best way to ensure a smooth PS4 experience is to use an ethernet connection, which is more stable than WiFi.