Very interesting! I suspect that this is either/or being caused by Nuxt, or our Pretty URLs feature.
Let’s start with Pretty URLs. I can see that ‘Disable asset optimization’ is not checked (therefore AO is active) and Pretty URLs is checked (therefore Pretty URLs is active) for this site. Using these reproductions, particularly this one, we can see that content won’t be duplicated across trailing slash and non trailing slash variants of your site.
This can be proven by navigating to https://admiring-curie-585c96.netlify.app/index.html and https://admiring-curie-585c96.netlify.app/index.html/ or https://admiring-curie-585c96.netlify.app/subfolder/ and https://admiring-curie-585c96.netlify.app/subfolder// for example. So, it doesn’t look like it’s related to this directly.
So, now I’m scratching my head. I can see that, in your deployed files, you have up to 4 subfolders. I’d be interested to see if, if you created a page such as /1/2/3/4/5/6/index.html, whether the number of slashes you required in order to receive a 301 status code changes. If the number of required slashes does change, this looks like a routing issue in Nuxt.
Lastly, I’d be interested to see what impact the following redirect rule has:
/* / 301
I suspect that it won’t change anything, thus leading me to believe that this is a routing issue with Nuxt. Interested to hear what we find!