The plate looks to have uneven buffing, some areas are more polished so react with the iodine more. Try to create more even buffing by keeping hte plate parallel to your polishing surface
Judging by the colors it looks like you have at least 3 cycles of iodide on one plate.
That is a lot more than one would expect from uneven polishing. Still it’s an important factor.
Is the iodine distributed evenly in the tray at the bottom of the box? Perhaps you titled it just before fuming. Or as Bakody advised you should wait a while (several hours) after charging the iodine to allow the fumes to distribute evenly across the surface of the plate. Check the plate frequently during fuming and rotate the plate to compensate for unevenness in the iodine fumes. Your box should be 5 to 8 cm deep to allow plenty of room for iodine fume distribution.
The distance between the iodine and the plate is more important than the amount of iodine in the box. The concentration of iodine fumes diminishes sharply with the distance from the crystals because iodine fumes are 8.8 times heavier than air. See post of 5 July 5 2011.