I have a mod chipped OLED Switch with a Partition based Emunand on a Sandisk (FAT32) 512GB SD, yet recently it seems to have issues booting, as it will get as far as the "Switch Logo" and then hang on a black screen after it clears. As a result, i'm forced to hold the power button for several seconds before I can boot it Hekete again.
Also, when it does boot into HOS, installed games seem to take longer to load than before and the overall SD card performance just seems sluggish than what it used to be.
The console was bought brand new 4 months ago, hardly used and still plenty of space on the SD with around 25 games installed so far. Nothing has been added, changed as far as I'm aware and in the beginning, it was flawless with no random boot hangs or longer load times. Could the SD card suddenly become bad? and would migrating the card to a new one fix it?
Sudden failure tends to be exactly how SD cards fail, but I don't think sluggish performance necessarily indicates a bad SD card. SD cards tend to fail in more spectacular ways.
Sluggish performance could be as simple as a fragmented SD card, but fragmentation tends to happen slowly over time and mostly when the storage is almost full, so it doesn't seem that likely in your case. Failing to boot could be completely unrelated to the SD card.
Do check the SD card info in Hekate and make sure the SD card is not running in 1-bit mode. A dodgy connection between the mainboard and SD reader board would cause all the symptoms you're describing. That connector tends to go bad after repeated insertions and removals. It could also cause random crashes (both in OFW and CFW) which tends to worsen over time. Normally Hekate should warn you if the SD card is in 1-bit mode (when you enter the Hekate menu) but it doesn't seem to do that every time in my experience.
It would be unlikely for the connector between the mainboard and SD reader board to go bad after only 4 months, but not impossible. The SD reader board is only held in place by a single screw, so that connector is stressed every single time you insert or remove the MicroSD card. Quite a big design flaw to be honest.
Running a chkdsk /F /R /X
E: (replace E: with the drive letter of the SD card) in Command Prompt to do a thorough scan of the SD card should rule out any issues with the SD card itself. This should be the first step after ruling out the 1-bit mode thing. If it mentions bad sectors/clusters, that's usually a bad sign, but a format could clear those up with seemingly no ill effects (although I would not trust a card that had bad sectors at one point even if the format does clear them up, it's likely there will be more, and the SD card I have that did have bad sectors that disappeared after a format seemed to be much slower than it should be so clearly it was still bad)
If chkdsk doesn't find any errors, there's probably nothing wrong with your SD card. It doesn't seem like a fake card, as you would've noticed games not installing correctly or coming up as corrupted when you launch them by now. Those fake cards usually only have something like 8-16GB of actual storage.
I think it could be worth copying the data off, formatting (as FAT32 64k cluster size for optimal speed and less risk of corruption compared to exFAT, use guiformat or Minitool Partition Wizard) and copying the data back on. Just make sure not to accidentally delete or format the emuNAND. You could always back it up with Hekate first to be safe so it'll be copied along with the other files. You should run the chkdsk first though.
It might not make much difference, but it couldn't hurt, and it'll clear up any fragmentation.
Side note, I have only ever had one SD card fail on me in such a short time span. It was a Transcend SD card that was only lightly used, which failed after only 6 months. But when it failed, it did so spectacularly. Everything got corrupted and the entire SD card was filled with corrupted file names. I've had other SD cards fail on me, but only after years, and they didn't just become slow. They had random silent write errors leading to some corrupted files that I only discovered much later, and one of them eventually went fully read only. If they did become slower, I didn't notice, I noticed all the other side effects first. Your case doesn't sound like a bad SD card to me, since you said it only fails to boot sometimes, which doesn't usually indicate corrupted data, and my bad SD cards never seemed to have issues reading, it was more writing that was the issue. But I have only experienced a fairly small amount of failed SD cards in my years, so take that with a grain of salt.
SD cards are absolutely not durable and they should be treated as disposable, but 4 months is pretty short. Could just be bad luck though.
