Nightrider / Nighthunter speed

I use a nighthunter/nightrider FL combo to plow through ingredient missions and the lower levels of some events.

Recently, I’ve noticed my +5 Nightrider commonly getting first turn over my +9 Nighthunter, despite Nighthunter’s higher base speed. Is this a bug, or do speed potions have a greater effect on legendaries than on SEs?

There is a random modifier

Try to change the position of the mons in the first 4 slots, this helps.