Are you able to put in a picture of your microflow? In order for an object to be available to an action, the creation and/or retrieve must be on the same line as the attempt to use the variable. Are the return values of the Java action appropriately set? Do you possibly have an exclusive split in your microflow that might divert your path?
It looks like you try to access a variable called 'LoggedInUser' in the exclusive split.
But you do not receive that variable before.
You have to get that variable before you can use it. Do you have some sort of custom logic to do that?