I just got my iPhone Pro Max replace 2 days ago. Had the original for only 3 weeks, with issues since I got it. I had sold off my old phone, so I couldn't send the new defective phone back, otherwise I would be without a phone (needed for work.) After 3 weeks, I just couldn't take apps randomly freezing. I'd open the camera, and it would be just black. I could switch between the different camera modes, but the view finder would never show what the camera was seeing, just a black screen. Opening Snapchat, the view finder worked, but when I snapped a photo it would look like a corrupt photo file (green/purple/blue/etc colored lines covering the photo.) I would be scrolling through the photos app; and it would randomly freeze. I wasn't able to scroll any further, could not switch between albums, etc. I could force close the app, but launching it again but still unable to scroll or navigate the app. Same for Google Chrome, Messages, Notion, Mail, Slack, and many other apps. They would just get stuck and no longer respond... Only way to gain access to them again is to reboot the phone. I was having to reboot 2-3 times a day.
Doing the basic troubleshooting steps on my own; I factory reset the phone several times. First time, I restored from iCloud Backup but that didn't fix it. Second time, I set up as new device, had to download all of my apps again, log into all of my accounts, and the other parts of setting up a new phone. STILL did not resolve it. So the third reset, I factory reset from iTunes - installing the OS all over again, letting it install whatever updates were needed, and then setting up as new device again. STILL Did Not resolve the glitching.
So I made the 1hr 15min journey to the only Apple Store in my state.. Spent and hour waiting to speak to a "Genius" only to have them replace the phone. Spend another 2 hours there, backing up my old phone, downloading the iOS update to the new phone, setting up the device, downloading apps, and etc. (since they let everyone in the store connect to the same wifi, instead of having a separate network just for those getting Tech Support so downloads/updates/etc will be quicker)
1 days after the replacement, and the P.O.S is doing it again! I was in the middle of checking out with my Apple Pay, when it stopped responding to touch. I tried force closing Apple Pay, closed all other running apps, but nothing helped.. So I had to stand in the checkout line, holding everyone else up, while my $1400 iPhone had to reboot because it doesn't f*ing work as it should.
Later in the day, I was trying to take photos of a special occasion and the stock camera app locks up. Luckily I had another camera app installed, so I was able to quickly switch over without missing any moments that happened..
I called the Apple Store back, and they said they only thing they could do was keep the phone for a couple days to have their "Genius" look for hardware issues. Its a new phone! That they f*ing gave me! WTF!
And FYI; Its possible this is a software issue, but this has been happening to me since I got the phone on the original iOS 13 public release.. and it continued to happen through the multiple iOS 13 updates Apple pushed out. So either the bug is somewhere in the software, that's not getting checked by Apple before release.. or their hardware is just defective.
PS: This is also happening to a friend of mine, with the same model phone - Only difference is the storage capacity.