Hi there... I just wanted to post a follow up.
Arriflex requires a certain threshold of continuous write speed from these cards (I think we all knew that already) so cfast cards meant for use in our cameras are built and tested to a certain spec.
It seems as if somehow a batch of "lesser" rated cards got mixed in early shipments of the Amira, and while they may work fine, performance can also be erratic. The SUP I installed now "filters" them out. One of my cards seems to be from this batch.
Oliver was kind enough to connect me directly with a supervisor at Sandisk, and I'm currently awaiting a new card.
If you post here, Oliver and Guenter do read and pay attention. They have been pretty active offline getting this resolved for me.