Photos.app no longer detecting SD cards for import

Lately, when I try connecting any of my cameras' SD cards, either through a USB-based SD reader or by connecting the camera itself, Photos.app does not automatically launch when the card mounts, and if I manually start Photos (either before or after inserting the SD card) the Import tab does not appear. I cannot find any settings anywhere for controlling this behavior, either – as the Photos Import tab isn't appearing I never have an opportunity to check/uncheck the "launch Photos automatically for this device."

I have tried formatting the card both from my camera (a Sony ɑ6000) and from my computer, and shooting in both RAW and RAW+JPEG – but to no avail.

This setup used to work just fine, and I don't know what's changed. What settings might I need to dig through? I know that in the past, SD card behavior was controlled by a bunch of different weird things (including iPhoto and Aperture, neither of which I have installed anymore). The device doesn't appear in Image Capture either.

What might be going on, and how can I go about fixing this?

EDIT: I should add, the SD card mounts just fine and shows up in Finder – it's just that neither Photos nor Image Capture see that it's an SD card with photos and/or video. The manual import process does work but I'd like to be able to import and erase all photos and videos in one step as I used to be able to (videos are especially annoying to do manually as my camera uses AVCHD which is stored in an opaque "clips" database).