2019-03-05, 17:43
My Fire TV Stick 4k got an update to 6.2.6.0 yesterday. The A/V async issue (180ms in my case) seems to be gone in Amazon prime video with auto refresh rate switching.
One bug still remains somehow, although they seemed to work on it (unsuccessfully): if the Stick is connected to an AVR the Auto refresh rate setting is not working after a reboot of the Stick. Though something changed since 6.2.6.0: the Auto refresh rate setting keeps being activated (cosmetically) in the settings, but without functioning. You need to change the Resolution manually in settings and change back to "Auto" for enabling auto refresh rate feature into a functioning state again.
One bug still remains somehow, although they seemed to work on it (unsuccessfully): if the Stick is connected to an AVR the Auto refresh rate setting is not working after a reboot of the Stick. Though something changed since 6.2.6.0: the Auto refresh rate setting keeps being activated (cosmetically) in the settings, but without functioning. You need to change the Resolution manually in settings and change back to "Auto" for enabling auto refresh rate feature into a functioning state again.