Wow that is strange. It should work. I just tried it and I have it working on my end. The only difference I can see is that I am getting the world location of an arrow (standing for your tank turret) and not for the actor itself.
Here is what I have:
Maybe plug some print nodes to the isValid outputs, to check if the reference is the cause for some reason? And also try to print the actor location again, it should be working.
And last but not least, check in your blueprint that on your actor tick tab you have “start with tick enabled” checked.
Might have been the cause all along?