I have a Plex server setup on a standalone Mac-Mini. It has an SSD and maxed RAM (16GB). The only thing running on it is Plex. My media is stored on an external Drobo "disk". I have a full Gigabit network in my house and a mesh WiFi with speeds that approach 900 Mbps anywhere in the house. Whenever I play content on my iPhone (Wifi) or AppleTVs (hardwired) I constantly get buffering freezes (spinning gold disks) and/or messages that my "Connection to the server is not fast enough to stream). Are there settings I should change with respec to transcoding or networking? Is there an issue with the iOS apps and buffering? The issue does not happen when I play a movie on my MacBook via the web browser though (on my local network).
Server:
macOS 10.12.3
Plex Server 1.3.4.3285