App is not connecting to server after restart on iOS

I have a strange problem.

I have disabled Hot Code Push (cause its sucks hard on mobile-devices)

I have set up my AWS EC2 with mup

when I create a
meteor build with --server=IP:PORT flag
or try it with
meteor run ios-device --mobile-server=IP:PORT -flag

my app is working like expected on first run and is connected with the server. It works also fine with testflight and so on BUT when I close the app and do a second coldstart my app cant connect to the server anymore. It looks like its changing the servers IPs so my app cant connect anymore.

any ideas how to fix this?