@Ouizer22,

I have seen some other articles regarding how FireTV devices do not always play well with the Roaming Options(wireless) and the Encryption Settings of the network, you can always try to change one of these settings to see if It is a small issue. Other users have also found success in using WPS to add their FireTv to the network and having them stay connected.

Otherwise, 

Have you tried to assign the fireTV a Static IP address while it is connected to the network, an address reservation in the router is recommended to accomplish this?

If the DNS server is lagging out, you can try changing the DNS server of your router to Google's default 8.8.8.8

Lastly, do the Router Logs or Firewall Settings Indicate any Issues that may have occurred during the disconnect?