Lua resty_dogstatsd only publishes first instance - lua

Question

I have a metric client that looks something like:
package.path = package.path .. ';../?.lua'
local metrics = {}
local resty_dogstatsd = require('resty_dogstatsd')
local logger = require('module.utils.logger')
local _statsd = resty_dogstatsd.new({
statsd = {
host = config.dataDog.host,
port = config.dataDog.port,
namespace = config.dataDog.namespace
},
tags = config.dataDog.tags
})
function metrics.incMetric1 ()
logger.debug('Updating metric metric1');
_statsd:increment(metric1 1, 1)
end
return metrics;
Then in my application I import it and use it
local metrics = require('module.metrics')
-- somewhere, some condition
metrics.incMetric1()
This publishes the log Updating metric metric1 in datadog and I can see it. But this will only publish the first instance. Until I restart service nginx restart, I will not get any more increments.
Update
So I have a start.lua in /etc/nginx/conf.d/start.lua that is:
package.path = package.path .. ';/path/to/my/app/?.lua'
local app = require('app.init');
app.start()
And the nginx config is
rewrite_by_lua_file /etc/nginx/conf.d/start.lua;
If I were to copy/paste the metric code into start.lua, then the metric is updated every time. Why is this?!
Update
I noticed this in the error logs:
2018/05/23 10:02:07 [error] 24483#0: *6 attempt to send data on a closed socket: u:some-hex, c:some-hex, client: 123.12.0.123, server: *.my-url.com, request: "GET / HTTP/1.1", host: "my.my-url.com"
This happens on the 2nd request to the nginx; the first time after restart, this is all fine ...
Update 2
This happens only if I have a metrics file and require it in my other. So if I instantiate the resty_dogstatsd client inside the main lua file, then everything is fine ...