I don´t think that you can push so high your intensity without getting stale shares. Can you show us your miner with stats? All over intensity 80 result in more staleshares - tested with 10 different AMD cards.
My Nvidia rigs runs fine with intensity 284.
It's not the cards, is the pool. Many pools pay for stale shares, and level 1 stales are counted as normal shares.
https://github.com/sp-hash/TeamBlackMiner/blob/main/FAQ.md