The same error has been reported by other users twice recently. Matej investigated it and made some code changes to prevent data loss: Warning: v2.4.3 corrupts model - #13 by Matej
You could also try regenerating the model: [Solved] Error: Object reference not set to an instance of an object - #4 by Matej
Could you use any hosting website such as Google Drive, OneDrive or even WeTransfer ?