Someone with better knowledge than me will jump in with more information, but I have noticed the same issue on my second (newer) account more these days.  My DT team there is the standard blender of increase attack (Spirit Host), AOE decrease defense (Warmaiden) and then nuke (Kael), and while the speed tune works fine on the first round, on the subsequent rounds Kael always goes first, which means that I don't have the buffs/debufs out to help.

I don't know what causes it either

Ive done the boss now, i switched rhazin into faster gear and started with bog down, but i dont understand at all why that happened, it has really confused me.

My guess is, Zavia have "Whirlwind of Death" mastery which adds speed up to 18.

Perhaps you have the mastery, which adds speed to the champ for killing enemies, which builds up over the first 2 waves?

Damn i should always think of masteries by now, its always masteries when i have timing issues on the game

Thanks, you are correct :)

Ah yes, that would make sense, and also explain why I never noticed it on my main account.  Masteries strike again!

Isn't there a mastery that increases speed that carries over rounds? This might explain @trevorwilson problem and yours.

yeh that was the problem, ive set up an auto farm that works now that doesnt even use zavia

Considering how long i have been playing, it is amazing how often i forget to check masteries.