Hey, please share 

• code that is causing the bug
• cluster access mode (shared or single user)
• runtime version

Are you using this methid to connect;?

https://docs.databricks.com/en/connect/external-systems/cosmosdb-connector.html

There is chance that the methond you are using is not supported with UC and you might need to upgrad your code or use No isolation Shared cluster.

e.g. i have been publishing FS to Cosmos DB with AzureCosmosDBSpec and i switched from:

• databricks.feature_store.online_store_spec
  to:
• databricks.feature_engineering.online_store_spec
  when I strated using UC as previous library was returning me bugs.