Failed to reactivate physarum backup

Hello,

Several months ago, I did a batch of slime mold backups. It was getting invasive and I used thick paper to conserve them. Unfortunately, recently, as I tried to reactivate them, the physarum on the papers became green-darkish and it didn't grow at all. I have the feeling they are dead.

So, I still had a small sample Ian, from this community, sent me before. I activate it and it grows now. So I'm really thinking what's going wrong?
Any advices?