Ok, I managed to play through
TP first time around and I got 59 Poe souls in doing so. I looked everywhere for number 60, and I checked guide after guide, rechecked every location, but alas no joy. Unfortunately that file can never be complete (for reasons I'll state below), but I'm on my second go through the game now (just finished Arbiter's Grounds) with 32 souls, and I noticed something interesting.
Poes exist in caves etc. all the time, but they only appear outside in the overworld at night (as far as I'm aware). So when I was in the Gerudo Desert I engaged a Poe in combat just as dawn was approaching. Now those sand creatures were taking my Z-targeting away from the Poe so I lost a good few hearts to his scythe, and by the time I had him on the ground exposing his soul the sun was very much in the sky. Naturally I clicked "Finish", but the second I pulled it's soul out the Poe disappeared (along with the soul) and I got no recognition of the capture. I personally think this is due to the fact that they don't eist in the daytime, but I still think that's a serious error if it can happen twice. I reset of course, and I didn't let it happen again, but has this happened to anyone else...?
What do you think of the Poe concept as a whole?