Your stats are session only when you're at a live table - this is by design since your opponents aren't going to know all of your lifetime stats and thus can't react to them. You can change these for opponents by double clicking their stats or by going to the PT Icon and changing them or by right clicking and ticking "session"; they should not be changing on their own.
If that's what you're seeing, please restart PT4 using the logging enabled link on your Start Menu, reproduce this problem and then report it via our
support system with the log file - that will help us figure out what is going on here and get it fixed for you. You can find that file by clicking File --> Show User Data Folder in the main PT4 window - the file we need is the text file called PokerTracker4 that is in that folder. The log will help us figure out what's going on so we can help you get things working properly.