Nginx response times got increased for unknown reasons

[Tamil Vendhan Kanagarasu]

Hello everyone,

We have been using Nginx for a few months now.
It was great until this week. For unknown reasons, response times got
higher.
Like 2 minutes, 3 minutes higher from what was < 300ms before.

No change on nginx configuration side.
Mostly, I use the configuration unchanged from apt install.
Only the following settings are added

```

# Max size of request
client_max_body_size 100M;

# Max request headers size
client_header_buffer_size 5120k;

#
large_client_header_buffers 16 5120k;

# Server name size
server_names_hash_bucket_size 128;

server_tokens off; # removed pound sign
more_set_headers 'Server: helptap.com';
```

The setup is as follows:
1. Nginx is configured to deliver some static files.
2. Nginx is configured to work as reverse proxy. Upstream
communications are done over websocket.
3. SSL is used for all communications. SSL is done using letsencrypt.

I timed the upstream & able to confirm that they respond with in < 50ms in
all the cases.
In the browser, I receive them many seconds and in many cases minutes later.
This issue is observed with both static file serving, http requests &
websocket messages.
So, I am sure that, it is not upstream issue, as static files also takes >
2 minutes to receive in one case.

Any help to understand and resolve the problem would be greatly helpful to
me.

Good day!

Best,
Tamil Vendhan Kanagarasu
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