No Vexes

I went looking for a woodland mansion today, using an explorer map. When I got there, I was killing vindicators and was startled by the trap-jaw thing the evokers do (didn't even see the evoker in the dark room behind the vindicator). But there were no vexes. The evokers had plenty of time to summon them (except for the one I sniped from the other end of the hall; he never even knew I was there) but none appeared.

I'm not complaining about the lack of vexes; I hate those things. They kill me more than the illagers do. But there should have been vexes in that mansion.