What brand are you using? Quality is one factor. We see a lot of bad "batches" and variation from pack to pack, and brand to brand. Turns out quality isn't strictly controlled if you read the fine print on the documentation. Additionally, higher ranges will do that to them. Here's an article that may help: https://www.thefabricator.com/thefab...right-tungsten

But overheating tungsten, which happens at lower amperages on an inverter will cause it as well.