I have a >10tb collection in Plex and stream to a Nexus Player (among many other devices, some over WAN) with zero issues. The biggest "issue" I've ever faced is that sometimes I need to lower my playback quality to 720p when I'm streaming over WiFi.
So glad I bought the lifetime Plex pass- I am happy to support the folks who made such a reliable and lovely product.
Generally speaking, if you are having issues with a product that is almost universally beloved by tens of thousands of paying customers, the issue is most likely on your end.
edit: The downvoters are going wild in this thread. Anyone who advocates Plex is being buried. For a moment I thought I was back on reddit!