First of all Sony came in picture in 2012 in regards to mobiles and Xperia X1 was introduced in 2008. Prior to that it was Sony Ericsson.
Now regarding your issues try repairing your phone as I have not experienced these issue after using the mobile for 9 months so far.
Here are answers to the points:
1. Messages hangs - When you open/unlock mobile and try to access the SMS received, it hangs, it is really pain when you are trying to do online transactions as it always hangs while getting the OTP on SMS. This delays or fails the transactions many times. Morever no confirmation of card swipe due to delay in rceiving as the app hangs. I tried the solution provided (Chrome update disabled) and do not want Google or FB to take over my messages as it will get all my personal info.
[PPG]: Are you using default SMS app or have you changed it to some 3rd party app?
2. Phone calling and phone book hangs - When you eant to call it invaraibly never opens. Many a times I have to go to Google voice assitant and voice command names of people I have to call. This is very inconvinient as I cannot call the numbers not saved in my mobile.
[PPG]: Never experienced this problem but some users are experiencing delay in call log.
3. Camera heats up for no reason and diables all its functions.
[PPG]: Use of camera at higher resolutions makes processor heat up and to cool down it disables some of the functions. This is epected behaviour.
4. Mobile lock opens in pocket if I have other app lock such as Truecaller or Slide
[PPG]: Don't use 3rd party app if that is causing any issues or follow up with these app developers to resolve this.
5. Battery issue - Runs out of battery in 6 hours, charges slow
[PPG]: Check battery status and which app is eating battery; some 3rd party apps eat battry alot. Remove those apps.
6. While the call is on the backlight should be constantly ON, but during the IVR call or normal calls, when you need to dial numbers or do something on screen the moment you try to touch the screen goes dark.
[PPG]: This may be due to proximity sensor. Try not to come near upper portion of your phone. If proximity sensor is activated then screen goes black immigiately.
I hope the team looks into this and provides a solution.
For most of the issues repairing your phone using PC companion is the best solution.
