filter_complex with Multithreading hangs

**Describe the bug**
When using -filter_complex in with the multithreading version, the command hangs with no log
**To Reproduce**
1. Go to https://ffmpegwasm.netlify.app/playground/
2. Enable multithreading
3.Use config:
```
[
"-i",
"video.webm",

"-filter_complex",
"[0:v]scale=-2:1080,split=2[bg][fg];[bg]scale=1920:-1,crop=1920:1080:(in_w-1920)/2:(in_h-1080)/2,boxblur=luma_radius=min(h\\,w)/100:luma_power=10[blurred];[blurred][fg]overlay=(W-w)/2:(H-h)/2",
"-an",
"video.mp4"
]
```

3. Click run-> it gets stuck