Originally Posted by drno
I don't think there was a soul shard on the 5th floor
That's correct. From the 4th floor you have to teleport back to the 3rd floor, then back to another section in 4 before heading to 5.
There is a soul shard on 3rd floor, but you have to go to 4 first and double back for it. There isn't a shard on 5. There is a separate thread with a map for Mysterious Union, and it's incredibly helpful.