@Pranav_Patel, retrieving and updating still successful for me.
Like it was suggested before, create new app, import there your table and try to run your code. If the problem will still exist, maybe start with hardcoding updated values and then updating exact value not in cycle.
I removed the stockupdate table. Created it from the console,added schema and then imported the data and now its working. So its reasonable to say the error was on your side. Please try and send some notice before making changes that affects the users, so that we are better prepared for it.