I have a Canon Rebel T7 and a recently-purchased "onn."-branded MicroSD card with an adapter.
I purchased this memory card in preparation for vacation, and the first time I used this card (besides a test shot or two) was for an overnight timelapse (using an external intervalometer). (This was several days into the vacation, and I was starting to fill up my other SD card which I had been using.) I set up the timelapse in the evening, and when I came out in the morning, the battery had died (which was not unexpected). When I put in a fresh battery, however, the camera displayed a "Card cannot be recognized, please format card" message. I popped it into a Windows computer and got the "File system not recognized, please format card" message. Fortunately I've heard about photorec and had another SD card with me, so I removed the unreadable card from the camera and was later able to recover the images with photorec. I assumed that the battery must have died in the middle of writing and image to the card, which somehow corrupted the filesystem structures. So I didn't think much else about it once I had recovered the photos.
After re-formatting this card, I took some "regular" (not timelapse) photos and one timelapse during the day (where I was able to monitor and replace the battery as needed), and had no issues, all with the "onn."-brand microSD card.
However, the other night I set up another timelapse on my front porch using the same setup and microSD card. When I came out in the morning, the battery was still full and the camera displayed the same "Card cannot be recognized, please format card" message. Windows also was unable to recognize the filesystem. Another round with photorec seems to have recovered all of the images that were captured - everything that was on the card before the timelapse (including the previous daytime timelapse), plus about 100 images of the overnight timelapse itself.
At this point I started suspecting that the microSD card had bad blocks or some other corruption, so I formatted the card in Windows and ran MediaTester on it. However, MediaTester found no errors.
What should my next steps be to identify the issue? I'm suspicious of the microSD card, but the media tester didn't find any issues with it. I've had this camera for over a year and (until purchasing this new microSD card) have only used the 64GB SanDisk SD card that was bundled with the camera (and have taken many timelapses with no problem). If the microSD card is bad I'll definitely throw it out, but I'm wondering if there could be an issue with the camera at play here?