Anyone had success with bitrate heavy 4k?

Has anyone had success with bitrate heavy 4k movies playing smoothly?
I had another simple 720p TV show playing on another device at the time. (Both LAN plays)
Kept having buffering issues on Roku 4 with 44658 kbps bitrate media (its a beast at 63.4 GB). 2160p HEVC. It would play for 30 seconds and then buffer for 10 seconds. Sometimes it would restart the movie from beginning.
Network is hardwired.
Was running on single drive while 720p show was off RAID.

Not trying to report as a problem with Plex, just more troubleshooting on what might be my root cause.
Maybe Roku 4 (1st gen 4k model) buffer cache?
Would any logs show whether it was server or client?

I’ve never had an issue with 2160p playback on any files, some are around the 90-100gb range. They direct play on the Nvidia shield no problem. Dolby true hd, 4k etc all play seamlessly.

Are you sure the file was direct playing and wasn’t being transcoded?

Just looked back and it was transcoding!