When Toth jumps to Zorn it applies the Fearful debuff potential on Zorn. (( You can watch his buff/debuff bar, a countdown timer for Fearful starts the second Toth lands,)) If you damage Zorn and are below the 30 meter range during that time, you'll get the debuff and have to swap targets.
If this is the case, It's like a plaque on Zorn, How long does the Fearful debuff potential on Zorn last? Same as it does on players? If it's a shorter period, then it doesnt matter how close to Zorn you are as long as you attack Toth during this cooldown.? This may make it easier to just switch to Toth for 1 rotation during this period. The only time I have this problem is when the jump occurs directly after the circle phase, because sometimes the safest path out of them is forward.