What does this error mean?

This error means that an invalid value was inserted for a DynamicCompositeType.

Why does this error occur?

The DynamicCompositeType works like a map of a type to a value of that type. The types can be provided as a String (e.g. "IntegerType") This error occurs when Cassandra tries to parse one of those type but the provided string is not a valid UTF-8 string. This indicates that the value provided by the user is invalid.

How do you fix this error?

Verify the type passed is valid for the DynamicCompositeType. Ideally, you should migrate away from the DynamicCompositeType.