Long story short - If you suddenly have issues connecting an android remote app to your device, try this. Download a different remote app (like sure universal) , go through the wifi pairing process. And while the new app is STILL paired, pair your favorite app again. It seems to be a problem with the pairing code, once a new one is generated you shouldn't have any more problems pairing. I hope this helps someone. If you know of any other solutions please post it in the comments.
I had same problem connecting my phone(android tv app) as remote to my chrocast device. This solved it thanks very much. To quote the solution in simple words
STEP 1‐‐----‐--------‐------------------------------ On your tv/chromecast go to Settings-> Apps -> System apps -> Android TV Remote Service
Step 2-------------------------------------------------- Uninstall updates && Clear data