Affects Version/s: Minecraft 1.9.1
Fix Version/s: None
Java vs unknown atm (not at this desktop right now)
I have had a total of five various villagers disappear without prompting. Three were stationed in minecarts and blocked off by solid blocks and/or wooden slabs.
There was no way possible for a zombie or other hostile mob to kill them, no way to smother in a wall, and no invisibility potions were thrown at them
I did a quick search and am not seeing other reports of this issue (either that or I suck at searching but alas this is my first attempt).
This issue was first noticed shortly after this version's rollout and has been consistently experienced since.
This is being experienced on a multi player server.
TLDR: villagers are vanishing without prompt.