Based on the error it appears after you updated the version it updated your index which is not compatible with the API version you are using.
https://docs.microsoft.com/en-us/azure/search/search-api-versions
Based on the above link it seems the new version does not work fully backwards compatible. So you will likely need to make some changes to your code. That being said, it is hard to tell what changes need to be made without being able to review your code.
For the portion of the title that suggests -CRITICAL, if this is a critical issue for you then I suggest you open a support ticket to get 1:1 assistance right away. Seeing as you are an employee you should have the ability to open that ticket. Feel free
to ping me if you need more information.