Yureka Plus seems to have universal same in this aspect. It seems that the calibration method is the ultimate way to get the issue solved. To do this, here are the steps-
1. Open dialer on your phone.
2. Dial *#*#7769#*#* and wait. This is the secret code to access proximity sensor.
3. Select Start.
4. Bring your hand near the sensor. Do not touch it. When the menu says come near , place your finger on the sensor , remove it when the menu says Go away. Repeat the procedure for a couple of times and then select Stop and Exit.
5. Make call and check again. If still it fails, you may need to calibrate again.