Thanks for taking the time to fill out this Bug report!
I believe that this is working as designed. When you use Fill, notes may be repeated or skipped depending on the length of your pattern and how many notes are in the given range.
In your example, every 2 steps in a pattern of 128 gives you 64 steps to be populated, and a range of C2 to F5 gives you 41 notes to use which is why you are seeing the repeats. While trying to reproduce this, I was also getting duplicates of G2, C3, D3 etc replicated so not only sharp notes on my end.
I’ll close this unless there is something else to clarify