iPhone 15 Pro - ProRes LOG worked fine but now it doesn't - puzzled

I've shot several videos with the 15 Pro in ProRes LOG 4k/60 that looked wonderful when converted using the FreeLog free plugin with light color adjustment.

Now, suddenly, ProRes LOG doesn't work. I set the phone as usual, ensuring that the UCB-C connectors from the phone to a USB-C 3.2 hub and from the hub to an external SanDisk Extreme 1TB SSD and a Shure MV88+ microphone were tight, and that "USB-C" was displayed on the phone, indicating that the SSD was indeed connected.

However, after I pressed the Record icon, the phone didn't record a file - no error message. I don't see anything obviously wrong in the settings. I formatted the SSD as ExFAT between shoots. I'd be very grateful for any thoughts about this. I'll do more testing, but with a planned upgrade to a 16 Pro Mac upcoming, I would like to get the workflow running smoothly again. (And it is a lovely workflow! Despite the large files, everything runs so smoothly in post.) Thanks.