In theory they still do but coop staff seem to be particularly bad at it.
I don’t recall ever seeing expired stuff in Migros.
Where the “fill up from behind” is followed that’s unlikely to happen in the first place. But where that’s not followed, customers need to take off the recently-filled-up front and dig up the old ones, and that will take time.
So, you may actually be more likely to catch them later in the day in the problematic shops.
They should be more concerned about cleaning the floors and making it tidy than bothering customers paying high prices in Migros. Better go to Lidl.
Kassensturz (consumer program Swiss TV) brought up this subject:
Supermarket staff (including security staff) is not allowed to check your bag by law!
They can stop you, ask for your permission to check them. If you refuse they must call the police. They can also not physically force you to stay there and wait for the police.