Misunderstandings with Gigabyte RTX2070SUPER GAMING OC

Ryzen 5 3600 (4100 across all cores)
Msi x470 gaming plus max
Ddr4 crucial ballistix 2 * 8gb 3800 cl15
Be Quiet system power 9 700w

I changed the thermal paste on the chip here on the weekend
Everything seems to be fine, I turned on the computer, after 10 minutes I come back, and at my entire desktop is dotted with small white squares, so I rebooted the computer, turn it on again, and I can already see horizontal thin stripes. And in the place where he drove the cursor - they disappeared. I go to the GPU-z, turn on the benchmark, it runs fine, but almost all the frequency indicators and everything else disappeared from the table. I go to the dispatcher, I have error 43. And on the motherboard, the VGA indicator was on in the Ez-Debug display.
I climb into Google, they write different things. I mean plugging the power supply, resetting the BIOS, turning it on again and everything is fine. I drove for 2 hours in a lodge - the temperature did not rise above 66, I drove in osst, combaster, aide, 3d mark, everything is similarly good, and the same temperature. I raised the resolution to 2 and 4K in the test, and everything is fine too. Then I played all day, everything is fine too.
And I can't understand what it was, like artifacts, but later I did not find any problems in tests and games, and with the help of mats I checked the memory - everything is also in order.
But after all I changed the BIOS cards, because I heard that both the driver and the BIOS could show this, but there are a lot of opinions, someone says that the chip is khan, someone is a driver, someone that Windows suffers from garbage.
The day before yesterday a new driver came out, got up without problems, and installed it, while removing the old one through DDU. Bios put on the card the one that is extreme for this card.
Tell me now, what could be the matter?
If this is a dying chip, then why then all the tests passed with a bang, and already like a week and a half in games and tests all the rules. And I'm already thinking of merging the card.
And I also remembered that about three weeks ago. During the game, for some reason, the colors of the textures in the game changed dramatically. After that, the frequency of the card was locked at 1605, and the settings in the burner or somewhere else produced a black screen. It helped by removing the driver, and leaving the one that the Windows itself downloaded. And just recently there are some misunderstandings that I described above.
The card was not overclocked, not mined, only games. She worked in an undervolt, which made it possible to gain the required frequency at a voltage sufficient for this frequency. I applied thermal paste with a coefficient of thermal conductivity of 12. And changing the thermocouple on the card, I decided to change it to the process, taking it out and then returning it back.
In general, tell me what it can be, either all the rules, firewood is going crazy, or drain the card.