Client is not compatible and server is not sending a compatible format

[Stroller]

I don't see this in the thread.  Why use the web player instead of the integrated player?  I'm wondering if the android web player can't scale the video.  Your phone resolution is 1080p-ish and the video from the transcode is 4k.  A similar problem happens for people with older non-Android TV 1080P Chromecasts and the transcode output is 4K.

In the app, the web player is the integrated one.. That the thing. Otherwise I have Exoplayer (deprecated), and external. 

The playback settings used in the app are 1080p already, however, like you see in the screenshot, the transcoding is still operating at a higher resolution. So maybe like you said, it's a scaling issue from the integrated player, but also a server problem : it doesn't apply playback settings for the device I'm using.

If I use external (vlc) it doesn't transcode and don't work very well depending of the x265 file & this doesn't resolve the main issue with the default player.