Photos hangs when switching RAW/JPG masters

I use Photos on the Mac to manage photos I take with my mirrorless camera, a Fujifilm X-T20.

The workflow until today was more or less flawless:

Import photos from an SDXC card (UHS-I) in JPG+RAW, and then switch to RAW original in Photos.

Today, Photos just hangs when I try to switch original to RAW. Tried with one photo, 3 photos and more. Just hangs with the waiting window:

Normally the operation requires 10 seconds or so for a bunch of photos.

Since I have 25,000+ photos, I am using Photos on iCloud.

The only way to stop the operation is to Force Quit out of Photos.

Would love any ideas or recommendations.