Other than the price per share difference here are two other differences.
ISF 0.07% ongoing charge vs VUKE 0.09%. So ISF is a tiny bit cheaper
Methodology: ISF fully replicates the FTSE 100 with the same weightings as the index. VUKE uses something called optimised sampling so it consists of the FTSE 100 stocks but with slightly different weights to allow for more efficient tracking.
Neither method is better than the other and performance is pretty much identical.
Its most likely down to the timing of when the dividends are paid. Usually dividend yield is calculated on a 12 month look back. When looking at 2021 calendar year, ISF had a yield of 4.28 and VUKE 4.43
Difference here may also be down to rounding of dividends when distributed
I had vuke a while ago but sold my shares gonna go back in as i need to up my etf positions,i wouldn’t sell to buy the other although vuke does seem slightly better and i prefer vanguard over blackrock,and the yield seems a bit better.