My trip to the Apple Store went like this today. The technician did a diagnostic test on my phone and found nothing wrong. He then wiped my phone clean, and reinstalled the latest software. So far, so good. Hopefully it won't freeze again. It was nice to get out of the house. I was also able to pick up a new external CD drive for my iMac. My grandson borrowed mine, and he has had it so long, I told him to just keep it. His laptop does not have a CD dri So I killed two birds with one stone. My trip to the Apple Store took only 45 minutes going, but twice as long coming back.
The "nothing wrong" always gets me.
as someone who has fixed a ton of computers.
I can tell you that how someone uses them can actually tell you whats wrong.
For example. I've seen computers that NEVER fail when I use them, but as soon my friends or my client does a very specific set of pushes, actions, etc.. the computer just crashes!. (could be software error..)
Other cases are outside interference.
For example, using X wifi causes the wifi card to report error and crash the entire computer. Or the power in a condo is different than in the office (power and signal quality), which could lead to instability.
Temperatures is another factor, as well as dirt and humidity.
Could be that your phone has certain part of the memory corrupted, but only reached the corruption when you were using it in the way you did (example, your phone as 16Gb ram, the way you run programs uses 15gb and the 15th GB is damaged, thus crashes). But The expert as efficient as he is, will probably run a standardized test that wont reach even half of the memory. thus it will look "fine" for them.
Only a big long deep scan (like those PRIME or memory scan tests for hours that test PC stability) can reveal real problems that are pretty hidden in a very specific part of a computer.