Are you streaming from multiple devices, or just Plex?
If just Plex, is it a single library or is it multiple libraries? If you have the same title listed in multiple libraries they can appear as duplicates in Infuse.
With regard to artwork, do these items have artwork in Plex? One thing that can help is to either use the ‘Refresh Metadata’ or the ‘Match’ options in Plex to ensure Plex has the correct info for these items. Once this is done, you can try using the Refresh option in Infuse to pull down the updated info (or use the Clear All Metadata option in Settings to pull down everything).
Keep in mind, when using Plex (or Emby or Jellyfin) Infuse will use only the metadata/artwork provided by Plex, and will not attempt to fetch its own from TMDb/TheTVDB.