Hi André and thanks for the report! Oh, and welcome to X-plane, too!
Yes, we are aware of a parsing problem with the Navigraph dataset we are having... Tom is investigating that!
As for your disconnects, it is very hard to see what is going on without more info, screenshots or even better a short video. Some users had problems with setting the CWS deadzone too small (so joystick input would disconnect the AP), or flying past a discontinuity would also send you out of LNAV.
We are simulating an older FMC version, so the NG´s will not always compare to ours...
Happy flying, Jan