The “Return” node is usually added when a function is set up to return a variable of some sort - in this case, it looks like your “Spawn Player” function is set up to return a bool. To get rid of that, you should be able to select the function node and look in the details panel, where inputs and outputs are listed, and just remove the bool output.
An “Accessed none” error comes up when something in your graph is trying to read information from a variable that isn’t there. So somewhere, one of your “Set ___” nodes is either not getting the target it needs, or the target is getting destroyed (do you destroy the player pawn at some point?) and then it’s trying to get something from a variable referencing an actor that’s no longer there. I’m still not quite sure what’s going on from the screenshots you’ve posted, but I do see a “Set ___” node for a transform variable in your “Set Checkpoint” function that has nothing connected to it, so hooking something into that might remove one of the errors.
Unfortunately, the accessed none errors sometimes don’t list the correct node as the culprit (it’s in our bug database; hopefully will be fixed soon), so they can occasionally be misleading. One thing that might help is setting a breakpoint (select a node and hit F9) where you think the problem is starting, then using the stop buttons at the top of the blueprint to scroll through the sequences one step at a time until you see something that doesn’t look right.