This damn bug has been in the game since the beta...

You try to open the locker using cash and it keeps telling you there is a connection problem even though your connection is fine. Waiting or trying again does not solve the problem. In the end you have to proceed and miss the reward. You have no idea how many lockers I have missed this way...

And of course there is no way to reset your PVE progress so you get stuck with most PVE stages on high difficulty with no way to get any locker rewards...

Since there is no problem with your connection in the first place, everything works fine again as soon as you have gone past the locker phase.