Here are my observations concerning the new V3.865 update...

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USB installation … partly ok (see comments below)

Voice control after installation … ok

DTS Passthrough via AudioTrack API … not ok

2.35:1 stretch in Video app … not ok

USB write permissions … not ok

USB compatibility issue … not ok

USB storage not accessilbe after deep standby ... not ok

Double info OSD when switching favorites via DISCOVER … not ok

Guide channel list always reverting from favorites to full ... not ok

SideView app remote empty app list … not ok (reinstalling the app fixes issue)

The TV doesn't start the update automatically when plugging in the USB pen drive (tested with FAT32 and NTFS). Only Marshmallow's "open with" screen is shown. Only a complete reboot of the TV (power cycle or long power button press) with USB pen drive plugged in made the update start.

The update reverts the digital audio output option to PCM. In order to enable Dolby Passthrough, it might be necessary to set it to one of the auto options again.

Some of my USB pen drives, which worked properly under Lollipop, cannot be accessed under Marshmallow anymore. These are detected as SMI within Android's storage manager.

The Grand Tour on Amazon Video in 4K with Dolby Passthrough suddenly works much better for me. Amazon Video app is still the same version though (4.1.70). But the problem is not completely gone for me. Audio still slowly drifts off. But a single video frame glitch every few seconds seems to resync audio.

For further issues check out my bug tracker.