The running monkey is always hard to catch, but he does a loop, between the monkey chute room and the 5 doors room. Make sure and check the boardwalk balcony, and actually check the doors. (I found him 'stuck' to one of them a couple of times
Most of the time reloading doesn't help much. The last 3 or 4 times I did the temple, he actually started outside the gate when I clicked on the lever in the monkey chute room.
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..Good luck