i just turned back to my game after reading this and one of my researchers was going away in that exect same kind of way you said yours were doing so i thought that maybe you should...
STARVE THEM TILL THEY WORK WORK OR STARVE WORK OR STARVE!!!!
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sometimes i think hmm might as well check virtual villagers around this time and there always seems to be a pervert and 10 times more villagers to feed