Hi, I've been working with PC12 cells since 2022, and I never had a problem to attach them to a coated surface (I use PDL), but recently I started to use new vials, when I try to seed them in a 24 well plate, coated with PDL as usually, they are not attaching. Also I noticed that they are actually not forming clusters, I don't see any sign of contamination, an also when I first thaw them, I usually wait 6 days to start my experiments. What could be happening?