DiffuseMAVERICK , From a lot of forums I have read it is probably not a antenna issue. You may want to check through the links below before cracking open your phone to check the antenna.
Wi-Fi Issues- Potential solutions: From digital Trends link below.
You should always start with the easiest potential fix, which is to turn your router off and turn your phone off and then turn them both back on again.
Now try going to Settings > Wi-Fi and long press on the network you are trying to connect to, then tap Forget and set the connection up anew.
Take a look in Settings > General > Battery & power saving and check that Battery saver isn’t interfering with your Wi-Fi.
Check in Settings > General > Smart Functions > Smart Settings and make sure nothing in here is interfering with your Wi-Fi.
If you’re connecting to the 2.4GHz band then try 5GHz instead and vice versa.
Download and install Wifi Analyzer and check how busy your channels are. You may need to switch to a less crowded channel.
Check in with your ISP or router manufacturer and make sure that your router firmware is up to date.
If all above fails you have an option to performing a“wipe cache partition” see link #2 or a factory reset(will lose all data not backed up).
Turn off the LG G4
At the same time, hold the power off, volume up and the home button
After a few seconds, the LG G4 will vibrate once and the recovery mode is started
Search for the entry called “wipe cache partition” and start it
After a few minutes the process is complete and you can restart the LG G4 with “reboot system now”
Turn on the LG G4.
Once you get to the Home Screen go to Menu and then to Settings.
Select Backup & reset and then Reset device.
To confirm your choice select Erase everything.
Last link, tear down guide will show you how to open phone to check antenna, at step 4, 2nd picture. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
Desmontaje LG G4