Cubase SE deleted one half of an audio file on "add track"

This is the weirdest thing !
I installed a version of Cubase SE on an old laptop Win7 Home Premium 64bit , ASIO4ALL driver .
I did this so I could import my old CubaseAudioFalcon .ALL and .ARR project files … which works perfectly .

However …today I had set up a Cubase SE project to record a radio station overnight ( to capture an early morning show )
A very simple stereo recording , around 7 hours of audio WAV 44.1K 16bit stereo. That all worked fine , no probs .

Later I opened that saved Cubase recording to set a marker track for the radio show , which started around 3 hours in .
I had just trimmed the audio to the start of the show …then clicked on Add Track / Marker Track

Then Cubase crashed .

I then could Not reopen that .CPR file … endless loop , that project file obviously corrupted.
And when I looked at the audio file in my Cubase10 everything after the show start is missing …in other words when SE
crashed , it truncated the audio file to the beginning of the show ( where I had trimmed it ) .,…the show + what comes after is gone
…totally …the WAV file is now about half the size it should be. All I have now is the audio Before the show start , of no use to me .

So how is this possible ?
All I did was try and add a marker track .
Is “Add Marker Track” a know bug in Cubase ?
It totally makes no sense .

Has anyone in here seen this sort of thing ?

Thanks , Michael