That is so strange, a graphic card that plays video games but can't solve any blocks through mining? I can't think about anything that still causes that issue, so strange, it's good you are been sincere with buyers, many will definitely want to buy for mining, you did the right thing 👍

It's better you return the graphic card to the seller, I'm thinking that the gpu is been tampered with, return the card before it's too late, there is nothing I can think about than the gpu is faulty, it's not software issue but hardware issue, might be memory or chip problem

You better try running a heavy video game on the gpu first, if it doesn't work then the gpu is damaged, go inside a dark room and use a flash light to look at the back of the graphic card and look for any missing resistors, I'm guessing resistors are peeled from the gpu , I had same issue before and I noticed that a green little resistor has shift or peeled so I use soldering iron and led to fix it back and it works

You need to do a diagnosis to determine the cause. If the same problem appears on a separate computer with the stock settings, then warming up the memory will not help you.
On the contrary, you can break the video card.
I had a similar case, the video card passed the furmark tests, but an error occurred during mining.
Check it out in the game, for example GTA 5.

If you are talking about using heater machines to refit the chips on your graphic card it's better to go on youtube and watch a video how to do it so that you won't mess things up, watch the tutorial and follow the process, good luck

It thus sounds like memory chip problem mate, you will need a heater or hair dryer, there are tons of videos on youtube about how to revive a dead gpu, just insert that in youtube search and you will see many tutorial, also use GPU-Z software to check if all details wi display correctly

The card is defective, I hope you can return the card? If no then you need to bring it back to life yourself, first make sure you insert the card in a motherboard with no other gpu and check if it will display, if it displays then find a gpu benchmark tool to stress the gpu, if you are getting crashed then the card died due to overheat.

Well for starters your card is 580 but seems its been flashed with a 570 bios.  Get the right buos on the card to start with.

Does it have a small switch to a second bios?  If so see if the original is still there in second position.

It's always more difficult when information isn't provided.

"One of my RX580..." I assume means others are working using the same configuration and parameters.

Invalid shares are usually user error: wrong algo, wrong port, but if it's only happening on one card
it's a bad card.

Well, 'the game' has come to us, in your words.
If this is truly double-spend, it's really bad for Cryptopia in the first place.

We both lose, and the attacker can be proud he stuck his nose into a kids coin.

The database is updating, however the issue with Cryptopia may be the fact that they have more coins than they should (somewhere north of 400M were listed for sale before they paused trading), when the total supply was around 385M. This would explain the relatively massive volumes since the 25th or so (forked coins were getting cashed out as soon as possible) as perhaps Cryptopia's wallet ended up on the forked chain (I'm not sure the details of how all this works). So even though the network may be fine after re-syncing, Cryptopia may need to do something more to sort it out. Your guess is as good as mine on what that would entail.

That said, the dev has always responded to me quickly when I send questions, so I've been impressed with that.

It would be nothing to worry about, but too much pressure was on LeaCoin hash rate in a pool, and it forked.
When two blocks are found on the same time, it forks.

https://github.com/leacoin/LeaCoin/issues/2

The user is on bitcointalk, his pool news:
https://lea.thecoin.pw/ (Look at latest news, below on the web page).

Why worry.. Better be patient, as always.
The site Leacoin explorer ( https://explorer.leacoin.org/ ) says 'data sync in progress, please come back later'.