When I use the V4 Datalogger with K-Line protocol, there is never GPS and OBD output in one file. Sometimes only GPS and ACC Data, sometimes only OBD-Data, never both in one file. (I cannot say, when it records GPS/ACC and when only OBD, mysterious.. ) At CAN protocol everything is fine.
I had this problem too, if I've fixed it in my version by having the logger repeatedly try to reconnect to GPS. In the provided code, the GPS tries to connect on startup, if it fails, it never retries. I've fixed this in my fork, you can see the line where it tries to reconnect here: