Thanks a lot for your message, https://forum.step.esa.int/t/missing-some-pixel-after-band-math/36163
However, I highly recommend you to use the public forum always instead,
Coming back to your question,
First, As I understood from your shared screenshots, you’re using Landsat_8, for this reason I think there’s better and easier formula to calculate wetness index, which is,
j.rse.2017.12.012.pdf (2.7 MB)
Second, Important notes should be taken in your account whether using the formula I shared or yours,
A. For missing pixels , check up the resample method you followed, and before hand check up the original image!,
B. I think there’re many other parameters play substantial role in calculating the wetness index the vegetation, water content, and others, because most of the missing pixels within sea and onshore or coastal line area.
Mapping Crop Residue by Combining Landsat and WorldView-3 Satellite Imagery
My last piece of advice, Use closest day to the one you faced up missing pixel and try it out.
I hope the foregoing meets your demand!