I remembered that I used to have the same problems with my other Thinkpads e.g. a x200s a very long time ago. The solution was to disable 802.11n. I just did that options iwlwifi 11n_disable=1 with my Thinkpad T420 I am using right now. And it seems to work now! Since Thinkpads are kind of normal at this campus, is there any way to incorporate this into the distribution/upstream projects? Or even detect why this is not working and fix it?