Marshmallow update on LG G4 stops you from downloading strictly on wifi. I have tried 5 different phones and they all exhibit this "bug."
On my 5th try, I tested without Verizon SIM card and was able to download apps, update apps and download large files from web strictly on wifi.
To test this, I went to settings->Data usage->turn off mobile data, then click on the 3 dots next to the magnifying glass and put a checkmark on restrict background data. Once that is done, I am unable to download any app on wifi only.
I think Verizon put this in intentionally because when I first tested the phone, I didn't have any SIM card in it and was able to update fine. Once I put the SIM card in, I am unable to download on wifi only. This was tested on 2 other phones.
I have gone through 5 G4's in the last 10 days and all of them have this problem. Tried the following; new SIM card, new Google play account, clearing cache, starting phone in safe mode, and of course, new phones. The phones work fine on wifi until the Verizon SIM card is installed. Once that is done, removing the SIM card won't allow you to use wifi any more.
Can anyone disable the mobile data fully and let me know if you also have this problem?