didnt know about that with ebay but i avoid ebay by default. i got my 1080 from amazon by MSI . its rly odd tho cuz it seems fine at the start but ones the ingame population gets to around 150 my performance goes to hell
hmmm. okay. than you have a real gtx i guess (assuming you paid a few hundred bucks on that hell machine ^^).
a lot of problems can be the reason for that lag. i'm not a pro, but i can give ya some tips and ideas.
* maybe you have wayyy to many programs open
* you might be infected and someone uses ya gpu for mining (dunno much about it, but i guess it is possible; try to play the game without internet connection)
* wrong gpu driver
* shitty power supply, making your gpu and cpu throttle
* defective gpu maybe?
* the game itself could be corrupt a redownload helps => don't put it in a subfolder in the programs x86 folder)
* overheating
and some more issues i forgot.
what ya can do:
* try it without network first
* to be on the safe side, still do a clean up by using malwarebytes and other stuff.
* check out how high your base temperature is and how it gets when playing the game. you can check it out with gadgets (simply google it). if your temperature is off (like in my case where my cpu has 18 °C base temperature XD), you can check out at least your base temperature in BIOS.
* test your gpu with new games out like warthunder on high settings. if nothing weird is happening and your temperature is perfectly fine you don't have any overheating problems and your gpu seems to be doing fine. if not then:
*dust off your GPU and maybe get more coolers
* check out what net supply you have and how much power it actually gives. a 500W actually doesn't provide ya with 500W, it depends on it's efficiency and so on. ALWAYS buy a good net supply. those things are even more important than a good motherboard! calculate how much all your hardware consumes under usage (usb drive and hdd cost 10W each summa summarum). don't use benchmarks from nvidias websites...they are just wrong. get the benchmarks from real testers. if ya wanna know how good your net supply actually is, you can bet your luck on jonnyguru. with a bit of luck he tested your net supply.
* normally a pc will shut down if it overheats, but if you use programs like MSI you can force a gpu to throttle to not get even hotter. if it's really the case, as written above, get more coolers and dust off ya GPU and everything else in ya pc. don't forget to make some space for ya pc to "breathe", at least 20 cm between ya pc and an obstacle.
* assuming it's a game related problem you can ofc just redownload it.
* if it doesn't help, play the gmae on windows safe mode (all background programs are offline there).
* if it still stutters and lags you might wanna see if your drivers are up to date and if you have all important NET framework installed. dunno what ya need to play the game, but installing all of 'em doesn't harm ya at all ^^.
* last but not least, i heard of monitors and new gpus than can rerender game graphics. however this is a really heavy process. dunno, if gtx 1080 actually does it, but if it does, disable it.
that's all i can think of so far :/.