For some reason the SelfActor key was missing for me. Just want to clear out for people who’ll encounter the same problem: Reopening the project fixed this issue.
I had the SelfActor key but the values were missing after setting the key for PlayerLocation (in my case HeroLocation) and spent 45 mins trying to track down why it wasn’t working and the timeStamp was not moving, and then saw your post, and I said to myself, “no way that will solve the problem”, closed down the project reopened it and sure enough the values were working correctly.
Don’t you just love it when that happens 
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When you clicked the pure cast toggle, you are supposed to hit the drop arrow a little below to expose the const function and toggle that on too.
Ps. Adding a screenshot or two helps more.