This really seems to be Premiere specific. I've tested my 4, Ultra TV and Stick and don't have any audio sync issues. I've tested Amazon and Netflix, as well as my local content via Roku Media Player and Plex with no issues. I occasionally see audio out of sync on YouTube, but I'm more likely to blame the video in that case. Some of the recordings there are just terrible.
Nvidia Shield, Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.