David has sent me over to your topic, which seems related to my issue. viewtopic.php?f=1&t=153815&p=806045#p806045
I have also had the same chaos happen twice in the past few weeks.
I imported the audio from a 90 minute film into an existing Logic project, which has many existing audio, software instruments, midi objects and busses etc..
I did not make the connection to the film audio import causing the problem, probably because I think I did an audio bounce on the arrange window shortly thereafter.
Normally I import the film and its audio into the project before I start creating tracks and instruments to start writing, but this time I recieved a new cut from the film, which then required me to import it into an existing project.
Since I don't work this way very often, I don't know if this problem existed before my current Logic version (10.5)
I will do a test when I have some time to see if we can determine if this is the cause so that we can avoid it with a work-around.
This is really dangerous because, as we both noted, the undo function is of no help.
I make backups constantly, but that is not much help if the undo funtion does not capture the chaos so to speak.
If I can repeat the issue, I will write again on your thread.
If anone else has any insights, please share your wisdom!