YOLOv4-tiny: IOU stuck at 0 — what could be wrong?

I’m training a custom dataset (315 images, 27 classes) using YOLOv4-tiny on CPU and my problem is that even after a few hundreds iterations (790/5400), both detection heads (Region 30, Region 37) report Avg IOU = 0.000000. No positive detections yet. This is my first project with yolo and im having a hard time with it, can someone please help me understand, thank youu!