Client is getting a 400 Bad Request periodically when browsing his website via iPhone. Site is on the MODX Cloud. I never get it on my phone. Could this be a Mobile Safari issue? Network issue? iPhone version issue? Cache issue? I mentioned the latter because I found my phone needs to be turned off each day or the browser behaves weird.
Generally speaking a 400 error points to incorrect data being sent to the client (iPhone in this case) and will depend on what rules are being applied by nginx and MODX. If you want to share the site we can try to confirm the issue for you, but it's something you should bug support about.
As far as needing to turn off your phone, that's a common problem with poorly written software on your device, from the operating system to the browser. It's usually due to memory leaks. The software requires a block of memory to work, but when it's finished it doesn't properly release the memory for other use. After a while, all this "orphaned" memory takes up all your device's memory, not leaving enough free memory to keep working. Not too many years ago Firefox had a problem with that; closing tabs didn't properly release the memory they had used, so after a while, after opening and closing hundreds and even thousands of tabs, your computer just ran out of memory.
@AMDBuilder: I'll bug support after I confirm if the client actually turns off his phone.
@sottwell: I remember that FF issue. I had to restart my computer a few times for about a week or so. Poorly written software indeed. I find that turning off the phone helps. I don't have any 400 errors on my iPhone for the same website in question. Since it's a sporadic occurrence I'll assume if a network connection issue. Client is located in a mountainous rural area.