Talk:Phaedra/@comment-26896558-20151002111205/@comment-95.250.198.111-20151004014413

It's a bug: enemy's level scale with time and not with waves, this mean that the longer you need to clear waves, the higher levels will the enemies spawn.

For more info see this guy's post: https://www.reddit.com/r/Warframe/comments/3neb15/i_think_i_figured_out_whats_going_on_with/

TL,DR: clear waves as fast as possible to avoid higher lvls.