Transcoding 4K HEVC MKV Files?

I have tried so many different combinations and can’t get my Shield TV to ever transcode a 4K HEVC movie without crashing. Any client (other than direct play on the Shield which works but stutters sometimes) when trying to play a 4K video, fails the transcoding and causes it to crash. I just literally reset and wiped my whole Shield to try again. Updated to latest Plex Media Server (has failed on every version I’ve tried) - 1.12.1.4885 and still crashes each time.

Anybody else seeing this? I have a WD 8 TB USB 3.0 drive connected in the USB port with some 4K movies in MKV Containers. Some have Atmos others have True HD or DTS HD. Seems to fail on all.