Two things can cause this in IR:

1. Dust or debris on the optics/filter — dust can reflect infrared more strongly than visible light, so it may show up much more clearly in IR than in a normal photo. If changing aperture changes the size/appearance of the spots, dust is a strong possibility.

2. IR hotspotting from the lens/filter combination — bright circular spots in fixed positions are commonly caused by internal reflections in the lens and filter. These are called IR hotspots. They often stay in the same place even if everything is clean. Stopping down can make them more or less obvious, but usually won’t change their shape much.

To reduce the problem:

• Clean the front/rear lens elements and the IR filter carefully.
• Test different apertures to see whether the spots behave like dust or hotspots.
• If the spots remain in the same place, try a different lens or filter combination; some lenses/coatings perform poorly in IR.
• Avoid stopping down too far if that makes hotspotting worse.