Cannot redirect stderr to file in bash when using VMAF cmd

Question

After executing VMAF command

vmaf -r "r.Y4M" -d "d.Y4M" --threads=24

the result is outputted to the console

VMAF version 2.3.0
901 frames ÔíéÔáÇ 41.36 FPS←[K
vmaf_v0.6.1: 94.171817

I'd like it to be outputted to a file instead. I thought that redirecting stdout/stderr to txt file would be sufficient

vmaf -r "r.Y4M" -d "d.Y4M" --threads=24 &> result.txt

The result.txt file is created but it remains empty after executing the command.

I tried the same method for ffmpeg command

ffmpeg -i "in.mov" -c:v libx264 "out.mp4" &> result.txt

and it works fine. What am I doing wrong?