Hello! Maybe this will help- https://www.mathworks.com/matlabcentral/answers/377812-does-not-contain-a-valid-simulink-model-in-slx-format.
Also, certain enterprise solutions software encrypt all filed saved on their file system. These files when accessed are not automatically decrypted even on a system within the enterprise network.
If this is the issue, you can resolve it by right clicking the file and selecting the manual decrypt option.For example, when using the DataStax Enterprise Platform, you would right-click the file and select “DSE > Manual Decrypt”.