Amplitube disappearing from tracks

I have come across a peculiar phenomenom: Amplitube 4 plug-in on certain tracks vanishes all of a sudden. It has been used as an insert effect on the audio tracks. When I open the track insert effects view, the effect is not there anymore. Closing the project without saving and reopening it brought it back. First I thought I had somehow managed to remove the plug-ins by myself but then it happened once more. Now I had to resort to a Time Machine backup to get them back. Amplitube has not been blacklisted. I wonder what is going on.