4K video freezing streamed from Synology DS716+ on Sony 55XE9005

Hi,
I've registered a question in Synology forum stream , but according to forum member the issue should be related to client part (PLEX app on my Sony Android TV), than to server part. PLEX Client has been updated automatically and I see, that its version is 6.14.1.3753, and PLEX server version is 1.10.0.4523.
I'm playing videos directly from Synology DS716+ (RAID1 with two WD6002FFWX-68TZ4N0 disks inside) to my 4K Sony TV 55XE9005 with Android OS. TV is connected to TP-LINK Archer C7 v2 (firmware is the newest-2018-01-17) via WiFI AC standard (TV shows 866 Mbps connection) and NAS is connected via cable to 1 Gbps NIC. Router is hidden right behind the TV. I'm running PLEX server on NAS and playing videos via PLEX application installed on TV.
Time to time I experience video freezes for 4-5 seconds when playing 4K videos (take a look here ), but not all. It seems that video is freezing only when video bitrate is more than >60 Mbps, but maybe I'm overlooking smth. What is strange, that when video freezes, Plex doesn't say that it's not enough network throughput for streaming videos, what usually happens when it's not enough speed for streaming video file. Also, when playing video file NAS is not transcoding it, because I don't see PLEX transcoding service and CPU load is less than 5%.
I've attached logs collected on PLEX server. How should I collect logs from Client side properly? I was able to turn Network logging on and access it directly from TV, but I'm not sure if I've collected these logs correctly (attached too)... Maybe I should rerun the same test, but before running it I need to start Network logging on TV?
Could you please help me with investigation?