You need to add release 'release key hash'. Earlier, while you were creating a facebook basic settings you might have added your 'bebug key hash' in the Key hash filed. That is why it worked for debug build. Same way in order to make the app work for production / release builds, you need to add the release key hash in the Key hash field.
How to create a release hash key?
Use this below command to generate the hash key
echo your-release-sh1 | xxd -r -p | openssl base64
echo 44:4E:48:99:19:50:5C:1F:63:A6:0F:F6:A1:C2:31:E5:01:38:55:6D | xxd -r -p | openssl base64