See if there's an update for Google Home app.
Also, check for updates of any system apps on your Android TV.
You have to use the remote that's in the Google TV app now
Just noticed you're using an Apple device, not sure if this app is available for Apple.. Try the Google Home app instead there should be a remote there
Yes, it happens on iOS for some reason. I just close it and open it again, and again and again and it might work.. or not.
Try a third party app like CetusPlay or something else to see if it works. If it works then a reset is going to fix your system but if it doesn't then it's likely due to your android TV losing the ability to find the networks or devices connected. Internet will work fine but stuff like FTP or feature to use your Phone as a remote won't work if that's the case. I have used several Android TVs and TV Boxes and Media Centers so I have this experience. Try turning on FTP on your phone using an advanced file manager app and try to find the device on your network from your Android TV using a dedicated advanced file manager or webview tab. If it can actually discover all the devices connected to the network, then something else is the issue. Most likely other interference with the app like Location being turned off, etc. can also affect remote app for Chinese OEM apps like Xiaomi, etc. If it is unable to discover any connected apps and return no devices on the same networks. Then the problem probably can't be fixed as the issue is with either a faulty firmware update or untimely shutdown that caused the system to be unable to access the devices connected on the same network.
On your Android TV, is the Android TV Remote Service app updated to v5.1? Check Google Play Store for app update if you have disable auto-update.