Non si riusciva a trovare la chiave da nessuna parte

[Vito89]

How does ‘si’ function in this sentence?

Is this a pronomial verb or a reflexive?

[David755502]

I think this is an example of the si passivante.

I usually manage to confuse si impersonale and si passivante, but this sentence has an object, so I think it’s the latter.