If you've been paying attention, when Lens are on the attack, Onana gets back in position very quickly. Even on that goal he was merely a fingertip short.
When your RB messes up a basic as hell 2 foot pass and the opposition takes a first time shot, to complain the keeper was out of position is trying abit too hard to force the blame elsewhere.
If they our defensive line was 1 meter further back, Onana would have been too. He moves forward when the defenders do and back when they come back.
Wake up.