Yes, the forum I used to test was this one.

Will file issues on GitHub with videos/pictures soon.

Opera Mini: Categories take very long to load, clicking on a post turns the page blank most of the time.
LG webOS and Wii U browsers: Clicking on a category turns the page blank with only the top bar and loading indicator.
Nintendo 3DS/2DS browser: Works, but icons show up as boxes.

MyBB and PhpBB worked perfectly on all of them. It looks like NodeBB is just a little too complex for simpler browsers...

Opera Mini makes me really worried because a lot of people on poor data plans or phones use that.

I updated to v1.3.0 and now I'm getting a different error when trying to visit the forum

TypeError: Cannot read property 'loggedIn' of undefined
    at helpers.displayMenuItem (/home/myuser/nodebb/public/src/modules/helpers.js:20:44)
    at checkConditionalHelpers (/home/myuser/nodebb/node_modules/templates.js/lib/templates.js:269:76)
    at parse (/home/myuser/nodebb/node_modules/templates.js/lib/templates.js:424:15)
    at parseTemplate (/home/myuser/nodebb/node_modules/templates.js/lib/templates.js:133:14)
    at Object.templates.parse (/home/myuser/nodebb/node_modules/templates.js/lib/templates.js:119:11)
    at /home/myuser/nodebb/node_modules/templates.js/lib/templates.js:169:30
    at FSReqWrap.readFileAfterClose [as oncomplete] (fs.js:445:3)

Is there any way to convert a MongoDB database to Redis? Maybe that could fix it for @xidui.

That's not normal at all. Could you do ./nodebb log after startup and after MongoDB crashes? Should be weird messages in there.

@xidui Yeah that should be more than enough, my server (I have Redis though) has only 1,5 GB. What operating system are you using?

EDIT: Left my host's (weirdly chosen) username in

I looked into NodeBB's log and I saw this (upon trying to visit the forum):

1/11 10:38 [582] - error: TypeError: Cannot read property 'bootswatchSkin' of undefined
    at /home/myuser/nodebb/src/middleware/header.js:116:83
    at /home/myuser/nodebb/node_modules/async/lib/async.js:726:13
    at /home/myuser/nodebb/node_modules/async/lib/async.js:52:16
    at done (/home/myuser/nodebb/node_modules/async/lib/async.js:246:17)
    at /home/myuser/nodebb/node_modules/async/lib/async.js:44:16
    at /home/myuser/nodebb/node_modules/async/lib/async.js:723:17
    at /home/myuser/nodebb/node_modules/async/lib/async.js:167:37
    at /home/myuser/nodebb/src/meta/tags.js:110:4
    at /home/myuser/nodebb/node_modules/async/lib/async.js:726:13
    at /home/myuser/nodebb/node_modules/async/lib/async.js:52:16
    at done (/home/myuser/nodebb/node_modules/async/lib/async.js:246:17)
    at /home/myuser/nodebb/node_modules/async/lib/async.js:44:16
    at /home/myuser/nodebb/node_modules/async/lib/async.js:723:17
    at /home/myuser/nodebb/node_modules/async/lib/async.js:167:37
    at /home/myuser/nodebb/src/plugins/hooks.js:121:4

Is it the same as this?

TypeError: Cannot read property 'bootswatchSkin' of undefined · Issue #5145 · NodeBB/NodeBB

https://github.com/boomzillawtf/tdwtf/tree/da8af063aa7b8ef7ef6c779a29b5dc7c6aa8f2bd https://github.com/NodeBB/NodeBB/tree/9cd29409f8db97fe9b822a5904ec1d97ef3978ad MongoDB 3.2.10 22/10 03:16 [4122] - error: TypeError: Cannot read property...

GitHub (github.com)

Again, works perfectly without a subfolder.

@xidui Oh, it sounded to me like you were just setting up your site.

Is this very recent or has it always been like this?

You can't use Redis?

@PitaJ Already got a Namecheap (Comodo) certificate for a year. I knew about Let's Encrypt but decided to just use my domain registrar.

NodeBB worked fine on a subdomain. However, I want to use HTTPS instead of HTTP, and I don't want to buy 2 certificates (or a wildcard certificate), so I'm trying to move it from http://forum.mydomain.com towards https://www.mydomain.com/forum in order to avoid getting an "incorrect common name" browser security warning. But I can't get it to work.

When I try to visit it, I get nginx's standard message

An error occurred. Sorry, the page you are looking for is currently unavailable. Please try again later. If you are the system administrator of this resource then you should check the error log for details. Faithfully yours, nginx.

The error log (/var/log/nginx/error.log) says:

2016/10/31 21:59:26 [error] 159#159: *2 upstream prematurely closed connection while reading response header from upstream, client: MyIPAddressHere, server: www.mydomain.com, request: "GET /forum HTTP/1.1", upstream: "http://127.0.0.1:4567/", host: "www.mydomain.com"

This is my nginx config:

### redirects http requests to https
server {
    listen 80;
    server_name www.mydomain.com;

    return 302 https://$server_name$request_uri;
}

### the https server
server {
    listen 443 ssl;

    server_name www.mydomain.com;
    root   /home/myusername/www/mydomain;
    location / {
        index  index.html index.htm;
    }
    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }

    ssl_certificate /etc/nginx/ssl/mydomain_com/ssl-bundle.crt;
    ssl_certificate_key /etc/nginx/ssl/mydomain_com/mydomain.key;

    # enables all versions of TLS, but not SSLv2 or 3 which are weak and now deprecated.
    ssl_protocols TLSv1 TLSv1.1 TLSv1.2;

    # disables all weak ciphers
    ssl_ciphers 'AES128+EECDH:AES128+EDH';

    ssl_prefer_server_ciphers on;

    location /forum {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header Host $http_host;
        proxy_set_header X-NginX-Proxy true;

        proxy_pass http://127.0.0.1:4567/;
        proxy_redirect off;

        # Socket.IO Support
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
    }
}

This is my config.json:

{
    "url": "https://www.mydomain.com/forum",
    "secret": "mysecret",
    "database": "redis",
    "redis": {
        "host": "127.0.0.1",
        "port": "6379",
        "password": "mypassword",
        "database": "0"
    }
}

I'm sure it's something really simple and I'm just overlooking something. Could anybody spot it for me? Thanks a lot!

Like @PitaJ said, the theme doesn't work because that line misses a comma. Put a comma after that description line and the theme should work, assuming nothing else is broken.

It needs a mail server/address to send those mails from. By default NodeBB tries to use the SendMail application for this. As you don't have that installed (I assume) it gives that error. Personally I'm using MailGun (with this plugin) instead of SendMail for this, because SendMail is complicated to set up.