"Not found" error on startup

Having spent the obligatory several months of initial typing into my Plex server, all is working well except … when I first start it up I get a screen that says (triangular exclamation mark icon) followed by “Not found We’re having trouble finding this page. It might have been deleted. Go Home”
Selecting the “Go home” button or any of the other menu items above or to the left all work well so I don’t think this is a serious problem. I just can’t find how to fix it. Any ideas? Thanks.

I get this all the time when first powering up my Shield TV’s (Plex Client).

For power management I disconnect power to the Shield’s when not in use. So it seems like it takes quite a while for Plex to establish a connection on a cold power up. (other apps on the Shield don’t seem to have this problem)

So I have to wait several minutes before starting the Plex client.

Thanks but I don’t know what a shield is and I know I don’t have one.
Dave out