most camera lenses are not designed for optimal optical transmission of infrared wavelengths and many will produce pronounced central hotspots in the photos as well as loss of acutance (sharpness), loss of contrast and sometimes excessive flare. In addition, lens coatings might make a significant difference in the quantity (and possibly quality) of IR light that makes it to the sensor.
lenses will almost always produce a hotspot to some degree in IR, especially wide angle lenses with newer coatings
hotspots often become more pronounced at smaller apertures eg. f/5.6-16
the hotspot can appear worse when processed as a colour image. For example if your foliage is yellow and your sky is blue, the hotspot can show up as yellow in the clouds (where it would otherwise be blue or grey). Once you notice this issue it's hard to ignore it and even harder to fix than a b&w image.
if you get your camera converted to IR ask them to ensure infinity focus with your widest angle lens is achieved as a small increase in sensor to lens flange distance can make this lenses impossible to use
diffraction will start to impair IR image detail at apertures smaller than f/2.8 on Micro Four Thirds and at f/4-5.6 on full frame cameras so f/2.8-4 is probably the sweet spot for DOF and detail whilst minimising hotspots on MFTs and f/5.6-8 on full frame