Weird trasparency on assembly CREO

[IL_VERDE]

Hi everyone, I've opened an assembly made 3/4 years ago and before than today was normal (I've not opened it since a year or more), today I've opened it and it looks like this:

It has this strange transparency and I'dont know what caused it but if i go in the no hidden view style it shows only the correct lines.

The assembly is part of a family table and every model inside has this problem.

I've already deleted any aspect and it doesn't change anything, I've also tried to remove trasparency in the view panel, but it was already at zero.
All the PRT are solid and not surfaces so thats not the problem.

In addition if i go back with the model tree bar to the first component it has the problem, but if I go before it and insert a new component it doesn't have this issue until i go forward with the first component.

I'm struggling to find a solution, but it seems it's a BUG i don't know how to solve it.

If anyone has already experienced this issue/bug please help me solve it.

Thank you very much