since a couple of weeks i've the exact same problem. NO COMPATIBLE STREAM
Configuration: Emby-server on Synology-NAS. Emby-client on LG-tv or Emby-client on Chromecast connected to LG-tv.
I used this configuration without any problems for many months (years).
I'm sure that due too an update either for LG, Emby, Chromecast or Synology a couple of weeks ago the "no compatible STREAM" suddenly popped up.
Chromecasting to the Chromecast connected to the LG-tv causes the same prob