Ope, I found one last piece -- there's definitely an issue with references in the Admin console -- after adding these two extra sub-locations, I had an issue where some calls were now going to /myprefix/admin/admin-res and /myprefix/admin/admin-api, but needed to be going to /myprefix/admin-res, and /myprefix/admin-api

To fix this, I added two more sub-sub locations to the /myprefix/admin location, making my final nginx virtual server conf look like this:

server {
        server_name mydomain.net;

	listen 80;
	listen [::]:80;
	listen 443 ssl http2;
        ssl_certificate /certificate/path.pem;
        ssl_certificate_key /private/key/path.pem;

	location / {
		try_files $uri $uri/ =404;
		root /var/www/html/;
		index index.html index.htm index.nginx-debian.html;


		location /curator/ {
			rewrite ^/route/?(.*)$ /$1 break;  
			proxy_pass            https://127.0.0.1:2202;
			proxy_set_header        Host $host;
			proxy_set_header        X-Real-IP $remote_addr;
			proxy_set_header        X-Forwarded-For $remote_addr;
			proxy_set_header	X-Forwarded-Proto $scheme;


			location /curator/admin/ {
				rewrite ^/route/?(.*)$ /$1 break;  
				proxy_pass				https://127.0.0.1:2203/curator/admin/;
                                proxy_set_header        Host $host;
                                proxy_set_header        X-Real-IP $remote_addr;
                                proxy_set_header        X-Forwarded-For $remote_addr;
                                proxy_set_header        X-Forwarded-Proto $scheme;
			
				location /curator/admin-res/ {
					rewrite ^/route/?(.*)$ /$1 break;  
					proxy_pass				https://127.0.0.1:2203/curator/admin-res/;
                                        proxy_set_header        Host $host;
                                        proxy_set_header        X-Real-IP $remote_addr;
                                        proxy_set_header        X-Forwarded-For $remote_addr;
                                        proxy_set_header        X-Forwarded-Proto $scheme;
				}
				location /curator/admin-api/ {
					rewrite ^/route/?(.*)$ /$1 break;  
					proxy_pass				https://127.0.0.1:2203/curator/admin-api/;
                                        proxy_set_header        Host $host;
                                        proxy_set_header        X-Real-IP $remote_addr;
                                        proxy_set_header        X-Forwarded-For $remote_addr;
                                        proxy_set_header        X-Forwarded-Proto $scheme;
				}
			}
			location /curator/admin-res/ {
				rewrite ^/route/?(.*)$ /$1 break;  
				proxy_pass				https://127.0.0.1:2203/curator/admin-res/;
                                proxy_set_header        Host $host;
                                proxy_set_header        X-Real-IP $remote_addr;
                                proxy_set_header        X-Forwarded-For $remote_addr;
                                proxy_set_header        X-Forwarded-Proto $scheme;
			}
			location /curator/admin-api/ {
				rewrite ^/route/?(.*)$ /$1 break;  
				proxy_pass				https://127.0.0.1:2203/curator/admin-api/;
                                proxy_set_header        Host $host;
                                proxy_set_header        X-Real-IP $remote_addr;
                                proxy_set_header        X-Forwarded-For $remote_addr;
                                proxy_set_header        X-Forwarded-Proto $scheme;			}
		}
	}
}

Adding that the fix for this is adding additional sub-locations for `/yourprefix/admin-res` and `/yourprefix/admin-api`. 

With only a reverse proxy for `/yourprefix/` and `/yourprefix/admin/`, you get a bad login screen because it's not able to load a bunch of files and interact with the service on these other paths.

I've included a scrubbed version of my final nginx config below:

server {
	server_name mydomain.net;

	listen 80;
	listen [::]:80;
	listen 443 ssl http2;
    ssl_certificate /certificate/path.pem;
    ssl_certificate_key /private/key/path.pem;

	location / {
		try_files $uri $uri/ =404;
		root /var/www/html/;
		index index.html index.htm index.nginx-debian.html;


		location /curator/ {
			rewrite ^/route/?(.*)$ /$1 break;  
			proxy_pass				https://127.0.0.1:2202;
			proxy_set_header        Host $host;
			proxy_set_header        X-Real-IP $remote_addr;
			proxy_set_header        X-Forwarded-For $remote_addr;
			proxy_set_header		X-Forwarded-Proto $scheme;


			location /curator/admin/ {
				rewrite ^/route/?(.*)$ /$1 break;  
				proxy_pass				https://127.0.0.1:2203/curator/admin/;
				proxy_set_header        Host $host;
				proxy_set_header        X-Real-IP $remote_addr;
				proxy_set_header        X-Forwarded-For $remote_addr;
				proxy_set_header		X-Forwarded-Proto $scheme;
			}
			location /curator/admin-res/ {
				rewrite ^/route/?(.*)$ /$1 break;  
				proxy_pass				https://127.0.0.1:2203/curator/admin-res/;
				proxy_set_header        Host $host;
				proxy_set_header        X-Real-IP $remote_addr;
				proxy_set_header        X-Forwarded-For $remote_addr;
				proxy_set_header		X-Forwarded-Proto $scheme;
			}
			location /curator/admin-api/ {
				rewrite ^/route/?(.*)$ /$1 break;  
				proxy_pass				https://127.0.0.1:2203/curator/admin-api/;
				proxy_set_header        Host $host;
				proxy_set_header        X-Real-IP $remote_addr;
				proxy_set_header        X-Forwarded-For $remote_addr;
				proxy_set_header		X-Forwarded-Proto $scheme;
			}
		}
	}
}

By adding those sub-locations for admin-res and admin-api BOOM everything started working. Thanks to this 5-years-old conversation. Paying the solution forward.