@ArthurSalim 

Arthur, two possible solutions.  1.  Put one of the remote units as the main one.  They all have the same configuration so there should be no issue in swapping them out.  Make the current main unit a remote unit and see if it then successfully connects.  If the issue is replicated with the 2nd unit then the issue could be more on your main router's setting an you may need to contact that devices manufacture.  This would be option 2.  Work with Arris to see if there is any setting that is blocking the Deco in AP from communicting through it and to the internet.  

One other question is do devices connected to the deco still get access to the internet?

@Carl I have tried swapping them all out but all give the same error as for the question. Yes they all give connection to the internet as normal, for all intents and purposes i get my full speed and stable connection but i cannot acess them trought the app. The deco itself keeps its red light on the main one and the flashing red on all the slave ones.

@ArthurSalim 

When you are attempting to access the Deco in the Deco App are you connect to its network or are you connecting through another non-Deco network such as a work or LTE one? 

@Carl I have attempted both, one with data plan, one with its own wifi, i connect to the internet fine with both. Just not to the deco itself trought the app

@ArthurSalim 

The Deco app only allows access to people who are either signed into the "owner" account or a "manager" account.  Are you signed into one of these accounts.   Not the Owner account is the only one who can create manager accounts. 

@Carl definelly, i am using the same phone and app i used to create the network to start with, no one else except me has acess to the network app.

@ArthurSalim 

Okay.  Two things i would recommend trying.  1.  Log out and log back in to the owner account.  2.  Make sure the app if up to date.  If both of these check out and you have the ability to try to access the Deco from a different device like another phone or tablet.  If any of that fails then let me know.  We will need to collect more information and send it to our software team for research.