I forgot: I left the suspension overnight in the frigde after adding PEG/NaCl

You are using a fairly small volume so the pellet might not be visible. Just go ahead and drain well and then resuspend the "invisible" pellet and titer it. It might be there but you can't see it.

I m usually using 5x PEG/NaCl Solution (PEG8000 + 1.5 M NaCl) for foodborne virus ; so by reading your protocole I have a few observations:

- Your NaCl concentration (2.5 mM) is so low.

- Adding 2.5 ml of 20% PEG to 10 ml lysate results in around 4.5% PEG final concentration which I see its low.

- I read your comment about the incubation since its necessary, but the gentle mixing its important as well during the incubation for some amount of time.

- A tip I usually doing it: sometimes the pellets may be invisible depends the samples I got, so I use a trick to mark the place on surface of the tube where it should be after centrifuge and from there I resuspend the pellet with PBS.