Is this Bug? Cheat? Or just no Luck?

I missed 9 attacks nearly in a row (with 5-Speed, 4-Speed, 3-Speed, and 2-Speed) to only 2-Speed with Flying (Shieldbearer).

And the enemy 1-Speed with Flying (Cave Slug) never miss my 5-Speed (Spark Pixies) and 4-Speed (Fire Elemental).

Theoretically this can still happen, but this makes me think: what is the percentage?

Can anyone share the formula to calculate hit/miss ratio for Flying and/or Speed?

Thank you.