Photos and videos vanished from "second space" on Xiaomi Redmi Note 9 Pro

I have (for 2 years) the "second space" in use (Xiaomi Redmi Note 9 Pro, MIUI 12.5.8.0 RJZEUXM, updated about 1 year ago), and it works wonderfully - two separate phones in one. But because I couldn't use the SD card in the second space and so lack of memory, I finally mounted the card as shared memory the week before last. Yay! Much more memory! But, a few days ago, the system deleted all pictures and videos in the second space that I had made since then (kayak tour). But only in the second space; the ones in the "first phone" are all there. I hadn't changed anything before, no reboot either (except after the incident, but I didn't do anything). Various undelete apps found nothing; the memory card can't be it. Took a media scan also, but nope. So: 1. How could this happen on the part of MIUI and 2. How can I (maybe, hopefully) get my pictures and videos back in second space?