limit_req at server level gives 404 error for files rewritten at location level?

[J.R.]

> In particular, if limit_req uses a map with regular expressions,
> this might result in $1.$2 to be set to something completely
> different from what was expected from the location matching.
>
> The general rule is: avoid using positional captures from regular
> expressions in location and server_name matching, these can be
> used only in very simple configurations.

You were right! I forgot I had a map matching /24 of the
$binary_subnet_addr that was being used by the limit_req_zone
directive.

I went through and gave names to my capture groups just to ensure this
type of conflict doesn't happen again.

Thanks again for your help!