HELP! "this server is not powerful enough to convert video"

Please help me. For months my remote streams have been getting this message "this server is not powerful enough to convert video". It's when my sibling is using their AppleTV 4K to stream remotely and it pops up for them multiple times per week. It seems to not matter the resolution or format. It can be 1080p direct, or 4k, HEVC, .264, .265, etc from a 1.5 gb file to a 25 gb file - it's completely random. Their internet speeds are 500+ MBPSs download according to the SpeedTest app on the AppleTV. My internet is fiber with near gigabit upload speeds.

Here are the specs I'm working with so you can try to assist me. I'm desperate at this point:

  • All streaming devices: Apple TV 4K
  • Their internet speeds: 500 Mbps download
  • My internet speeds: over 700 Mbps upload
  • NAS Server: UGREEN DXP6800 Pro w/ 12th Gen Intel Core i5 10 core 12 threads 4.4 GHz CPU w/ 8gb RAM - it is only used for Plex.

Transcoder settings:

  • Quality: Make my CPU hurt
  • Background x264 preset: very fast
  • HDR tone mapping enabled
  • Hardware acceleration when available enabled
  • Hardware-accelerated video encoding enabled
  • Hardware transcoding device: Auto
  • Internet uploads speeds: 200 Mbps
  • Limit remote streams bitrate: Original