Is Matthew 26:32 and John 20:9 a mistake stating that Jesus told the disciples He would rise again then stating they didn't know after it happened? Matthew 26:32 Jesus tells the disciples that He will die and rise again.


  But after I am risen again, I will go before you into Galilee.


John 20:9 says that the disciples didn't know that Jesus would rise again? 


  For as yet they knew not the scripture, that he must rise again from the dead.


Is this a mistake?
The fact that someone is given information does not mean that they know nor understand, nor realise its significance.  This is a perfect example.

John chooses the verbs here rather carefully.  Koine Greek has two words (verbs) that are translated "know", namely, (a) ginosko, and (b) oida.  W E Vine (Expository Dictionary of New Testament Words) comments on the difference in the shades of meaning between these two words:  "ginosko frequently suggest inception or progress in knowledge, while oida suggests fullness of knowledge".

In John 20:29, John uses the verb "oida" meaning that while the disciples may have known (been told), they did not fully realise the significance of what Jesus had said.  This is yet another reminder that the disciples were very human.