Related patch note from Patch 1.4 (December 2018) - [PC] Vermintide 2 - Back to Ubersreik - OUT NOW!
We’ve changed how random missions are selected for Quickplay. Our previous implementation led to some unfortunate situations, such as getting the same mission twice in a row. Our new mission selection algorithm is much more random, but will make sure you will probably not see the same mission come up twice in a row, as recently played mission are heavily discouraged by the algorithm.