Blocking in H.265 Export

[Selur]

My first suggestion when reading your post is:
Rate control in 'average bitrate (1-pass)' isn't that good.
Do not use 'average bitrate (1-pass)', better use 'constant rate factor (1-pass)'.

That said, the blog entry mentions:

...
Encoding Mode: Average Bitrate (1-Pass)
Target Bitrate: 18,000 - 50,000 kbps
...

while handling, 4k content, so keeping that in mind while using 6k instead of 4k it seems to be obvious, that the lowest bit rate encouraged to use for 4k might be to low for 6k.
-> If you want to stick with 'average bitrate (1-pass)' (against my advice), you will have to use a higher bit rate.

Cu Selur