Hmm looks all fine to me now and don´t worry about the OnlineSubSystem that usually wont screw you over.
MyController_TopDown for some reasson he fails to find his SuperClass and DefaultSubObject.
Can you make a Backup of your Project (just to be safe) and than try to reparent that BP to “Player Controller” under the Class Defaults. Save and Compile and try again. Im not certain if that BP will pick up the change since you reparent to the same thing. But if that did not Work try to reparent to “Debug Camera Controller” and than back to “Player Controller”.
And if even that did not Work delete the BP Completly and replace refferences where you used it with the simple Player Controller. That is just to confirm thats a faulty Blueprint or otherwise got corupted in some way. In that case you most likely have to recreate it (or if you use Version Control roll back to a working Version)