In thick plate (1" or more), this is catastrophic. The crack is often followed by a loud "ping" and a visible gap of 1/16" or more.
Mark picked up the piece. The edge was smooth. The hole was round. He ran his thumb over the cut face—no slag, no dross, no fissure. sheetcam hot crack
Sometimes a "crack" is actually just the torch piercing too close to the cut line or the kerf being set incorrectly. If the kerf width is too wide, the torch may sit on the edge of the material too long during the lead-in, creating a hot spot before the cut even begins. In thick plate (1" or more), this is catastrophic