Recurring file transfer issue that's causing serious problem

For the past few months we've had an issue maybe 1 in 20 times when transferring files after a shoot. The transfer will freeze, the error "This file cannot be transferred, it is currently in use" will appear, and the computer will be bricked for about 15 minutes. Finder will totally freeze and the computer won't be able to shut down until the card is removed or ejected (which is sometimes impossible.)

We thought the problem was the cards, but we've ordered in a new batch and the exact same error appeared again. The error won't replicate, trying with the same card on a different computer and the transfer will go grand.

We're shooting on a URSA Mini Pro G2 and recording onto a SanDisk Extreme PRO 256GB. We're transferring files with a SanDisk pro reader, but I've had it happen with different readers so they're not the problem. I'm transferring straight into a folder on a NAS from the card, but we also think we've had it happen once going straight to an external drive. It's also happened on multiple different machines, but always macs. Any help in trying to find the cause of this issue would be appreciated.

How are those cards formatted?

Just my experience with the Sandisk card reader is that at some point in time, it will start causing transfer errors on one or two of my CFast cards, usually the 256Gb or the 512Gb, but never on the 64Gb or the 128Gb which I have a few. It never is consistent but it happens. Since I used the Angelbird reader, I never got the problem with it reading/writing to any cards, including the Sandisk Extreme PRO. IME, I attribute the issue with the Sandisk reader or the cable that came with it. However the Angelbird has the same type of cable too, probably better quality (IDK).

you should turn off the indexing by spotlight for this device