I have fresh spigot build 2059 without any other plugins and burning don't add blindness to player. It just add icon of blindness, but vision is normal. I tried to adjust duration up to 200 ticks, but it doesnt matter, no more manipulation were done with config, I tried to complete reinstall server/plugin. Version of extra hard mode is latest from official spigot page of the plugin - 3.13.1-59445b0.

/version (img) https://i.gyazo.com/fe1a0ea1fb52ae94b945ed324bef0090.png

Still should paste config anyways, you may have changed something and not know about it.

``` 
paste the config inside backticks
```

Also missing output of /version extrahardmode

https://ufile.io/hyide config
/version extrahardmode

https://i.gyazo.com/3b8dbb6a20f933a7a0b1bd9223f3aa48.png /version extrahardmode

just paste the config here, or in gist.github.com. Not that file downloader junk.

Can you paste in http://gist.github.com or directly here in a comment? Makes it 500% more likely I'm going to revisit this issue sooner.

Link has expired, so yea, definitely need a paste.

Seems blindness was once a hardcoded potion effect for burning and was later removed (by Diemex when he still maintained it). However it's still applying the potion effect as per the config...

I'm going to guess it's incorrectly placed in the config. Perhaps the default config is incorrect, if you're using that - but we won't know until we can get a snippet of that config in here.