I started to have screen retention problem too. I have this device since February. I must say it's a really hard experience changing opo for g5 but I enjoy the phone.
So.. I found that this retention is weird, because it doesn't show when in locksceen. It looks like something like adaptive brightness turning on day mode or sth like this and then screen retention shows up.
I found even on max brightness sometimes locksceen doesn't show retention, also on bootanimation there is no retention .
IMHO this is software problem. ( I know lg is not good at software

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---------- Post added at 07:28 PM ---------- Previous post was at 07:20 PM ----------
Then i guess i will have the same problemagain after some months...
This phone is perfect but it has major issues with screen and gps and a smaller one with the audio Jack because mine when i have headphones connected some times it starts playing by it self
Yep Jack has some problems in detecting what is connected.. especially aux cables I must plug cable 2-5 times it'll start to work... When it not detect aux I only hear loud hissing ... I also think it is kernel problem I saw sth like that on other phones too..