something like that happened to my jtag once. everything got corrupted for unknown reasons. I managed to fix it, but it took a while.
I got NAND corruption on a legit switch. I had placed mega man legacy collection in sleep mode. when I came back to it, it said, "a serious error has occurred." it said to power off the system. I did that, but when I turned it back on, it wouldn't boot. it was still under warranty luckily. Nintendo said that the NAND got corrupted, so all saves were lost. since it was legit, there was no backup.
I've gotten all my saves back to where they were except octopath traveler (over 100 hours I believe with one chapter 4 left) and xenoblade chronicles 2 (I think 35 hours or so). because of what happened, I immediately got nso when I got the switch back. this was about a month in to nso, and I remember Nintendo asking if I had nso to get my saves back.
I'm not too mad about xenoblade chronicles 2, but I was so close in octopath. I wanted to see what happened when you completed all the chapter 4s. I was also a little bummed about odyssey (had 400-something power moons), but on my new game I have 842! and, mega man x6 was a nightmare the first time trying to save all reploids. it was still a little hard, but much, much easier the second time.
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btw, if you wanna hear a funny story, I do a lot of reading about consoles and their hacks. well, I read one article by one of the repair techs for microsoft who said that he was able to buy a new car due to all the overtime he was getting because of rrod. lol I think he said that they were at one point getting thousands of systems a day.