Rawrcake

Yeah this is intended, these creeps have an ability that increases their movement speed for a short amount of time. It looks like they're trying to catch up because they use this ability at set points rather than all at once.

I had a (somewhat) similair case on wave 16 where one of the dark immortals got 'stuck' on the exit portal and did not continue untill I built a tower nearby to shoot it.

I would love to help out. Rawrcake.184 on EU