2nd pass won't start..."file size too small"

[Selur]

Bug has been fixed in x265 since end of November (https://bitbucket.org/multicoreware/x265...f5c4e02ac7).
Running:

ffmpeg -i "F:\TestClips&Co\files\test.avi" -c:v libx265 -b:v 4000k -x265-params pass=1 -c:a copy "E:\Output\teste.mp4"

and then

ffmpeg -i "F:\TestClips&Co\files\test.avi" -c:v libx265 -b:v 4000k -x265-params pass=2 -c:a copy "E:\Output\teste.mp4"

works fine here, so the problem is with the FFmpeg build you use.
Seems like the FFmpeg build you use is build with an old libx265 version.

Cu Selur