Azure web app on Linux stoped working suddenly
Apparently, the maintenance you have mentioned is a Storage Failover (File Server Reboot of Volume Path Change), when this happens your the platform switches your application to a secondary storage.
Not finding the needed files to startup is something that happens sometimes with .NET Core apps due to the build process not finding the correct DLL to run while the app is still starting up.
In the meantime, specifying the DLL to be run in the startup command would be a good approach to avoid this issue happening again.
In the Portal -> Configuration -> General Settings -> Startup Command:
dotnet example.dll