I'm in the same boat since ~v5.11 (beta):
5.10 (and lower): works
5.11 (beta only): didn't work
6.1 (and higher): didn't work
Last working version is v184.108.40.2063, something after this got changed.
I've already posted an issue in the beta forum ~1 month ago about this issue, so far I can say, that v220.127.116.113 sends the following to Plex Media Server (on disabled direct play):
[0x7f1ee27fe700] DEBUG - Completed: [192.168.0.197:39574] 200 GET /video/:/transcode/universal/start.m3u8?audioBoost=100&autoAdjustQuality=0&directPlay=0&directStream=1&directStreamAudio=1&fastSeek=1&hasMDE=1&includeCodecs=1&location=lan&mediaBufferSize=74944&partIndex=0&path=%2Flibrary%2Fmetadata%2F7641&protocol=hls&session=c8b492eb121c1faf-com-plexapp-android&subtitleSize=100 (11 live) TLS GZIP 34ms 489 bytes (pipelined: 1)
Starting from 6.1 it sends:
[0x7f1ee27fe700] DEBUG - Completed: [192.168.0.197:58919] 200 GET /video/:/transcode/universal/decision?audioBoost=100&autoAdjustQuality=0&directPlay=1&directStream=1&directStreamAudio=1&fastSeek=1&hasMDE=1&location=lan&maxVideoBitrate=200000&mediaBufferSize=74944&mediaIndex=0&partIndex=0&path=%2Flibrary%2Fmetadata%2F7641&protocol=*&session=c8b492eb121c1faf-com-plexapp-android&subtitleSize=100&videoBitrate=200000&videoQuality=100&videoResolution=3840x2160 (7 live) TLS GZIP 36ms 1642 bytes (pipelined: 9)
Whatever you setted in the settings.
But there isn't any reaction from the devs, yet.