random problem with unable to pick up incoming call

[sonysw]

I am having random problem with unable picking up incoming calls. It seems the phone when to sleep. Either I pressed the pick up button or slide the answer screen, there is no response and after that I have a missed call. When I test the phone it seems fine but I end up missing phone calls do to this issue. Anyone has the same problem or know how to fix it ?

I am using 6.5 Sprint OEM ROM with the 6.5 tweak/clean up. Thanks and I appreciate your help.