I'm using Nicehash software for mining too but I'm not getting that number of rejected shares, in your case it's pretty bad , way too much of rejected shares, click on the Nicehash software settings and change location to nearest country, you should get lower rejected shares this way, Nicehash got a big problem on their hand
could it be about on OC ??...
Yes, 100% it can just be this. I've had this issue with my 3070, 100% tied to my memory clocks. When I push it too hard, I get rejected shares, but sometimes it takes several hours to show up. I use Phoenix Miner on Ethermine.