I'd like to suggest you take a look at @flannelist's excellent wiki article on what's called a kernel panic; it's basically an operating system function that happens when it runs into an unrecoverable error. When one occurs, it logs the error and reboots the phone, which sounds quite a bit like what's happening to you.
Read through to the part that tells you how to retrieve the panic logs and pull up the most recent one you find. Copy and paste or take a screenshot of the first page of that log (we don't need the whole thing) and come on back and add it to your question.
[guide|21499|Adding images to an existing question - iFixit Repair Guide]
Once we have the panic log, we can use that information to figure out exactly what is going on with your phone. If you want to try and puzzle it out yourself, the error information that's going to be usable will be documented on the SMC Panic Assertion wiki page, but we'll be happy to apply our experience and expertise to whatever you find.
So your job now is to check to see if you have panic logs (I'm fairly sure you will), then grab us the first page and come on back and show us what it says. After that we'll help you figure out what you need to do to fix that troublesome problem once and for all.
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=== Update (09/06/24) ===
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According to the best information we have available (Apple keeps all this stuff under tight wraps), the SpringBoard error you're seeing is generally considered to be a software error rather than hardware, although you're right that the weird heating issue doesn't seem like something a software issue should cause.
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Anyway, this kind of problem seems to have started with iOS 16 and the cure has generally been to update to iOS 17; of course that doesn't help you since it looks like you're already on the current release, iOS 17.6. So the next step, since you have a current backup, is to put the phone in DFU mode on iTunes and do a full restore of the OS. This is the most complete update possible and should get rid of any software issue you're seeing.
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I would suggest NOT restoring your backup yet, but just enter your Apple ID and try using the phone as is for a couple of days to see if the problem is gone. If it's still there then we'll be really confused, but if not we can be fairly sure it was indeed a software problem. Next step would be to restore your backup and see if the problem reappears.
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I'd say give that a try for a couple of days then come on back and let us know what happens. Alisha (@flannelist), do you have any other suggestions for Kat?
Hi Kat,
I'd like to suggest you take a look at @flannelist's excellent wiki article on what's called a kernel panic; it's basically an operating system function that happens when it runs into an unrecoverable error. When one occurs, it logs the error and reboots the phone, which sounds quite a bit like what's happening to you.
[[iPhone Kernel Panics|iPhone Kernel Panics - iFixit]]
Read through to the part that tells you how to retrieve the panic logs and pull up the most recent one you find. Copy and paste or take a screenshot of the first page of that log (we don't need the whole thing) and come on back and add it to your question.
[guide|21499|Adding images to an existing question - iFixit Repair Guide]
Once we have the panic log, we can use that information to figure out exactly what is going on with your phone. If you want to try and puzzle it out yourself, the error information that's going to be usable will be documented on the SMC Panic Assertion wiki page, but we'll be happy to apply our experience and expertise to whatever you find.
[[iPhone SMC Panic Assertion Failed|iPhone SMC Panic Assertion Failed - iFixit]]
So your job now is to check to see if you have panic logs (I'm fairly sure you will), then grab us the first page and come on back and show us what it says. After that we'll help you figure out what you need to do to fix that troublesome problem once and for all.