Here's the tips to solve your problem!
Method 1. Clear Cache on an Android device
If your device is Android 4.2 or above, this method will work for you (on older versions you might have to clear the cache on each app individually).
1. Go to Settings and select Storage
2. Choose “Cached Data”...
To ENABLE it.
1.Go to your LG Phone settings & find the (Screen Mirroring,Mirroring Display or AllShare Cast)
Enable that 3 if you have it.
2.Press source from your Samsung remote & You will find screen mirroring,wait until it connect to your phone.