Error Message example:

ERROR [CompactionExecutor:6] 2018-11-19 21:52:32,871  StorageProxy.java:775 - Error applying local view update to keyspace <keyspace>: Mutation

ERROR [MutationStage-1] 2019-04-26 14:29:30,357  StorageProxy.java:818 -  Error applying local view update to keyspace <keyspace>: Mutation

What does this ERROR message mean?

This means that the mutation for a materialized view was not applied to the local node.  It can be caused from a few different issue's. 

Why does this ERROR occur?

This error occurs because the mutation that is being applied is too large. This can typically be verified by a stack trace entry similar the following:

java.lang.IllegalArgumentException: Mutation of 115.157MiB is too large for the maximum size of 16.000MiB

How do you fix this ERROR

In order to fix the error you will need to identify from the above as to why the error occurred.  From there you can either reach out to Datastax support for additional help in resolving the error, or take steps to resolve the issue on your own.  In the above cases, one would be to reduce the size of the mutation being applied.  You could also increase the commitlog segment size, but you will want to be careful as this could lead to other issue's in the cluster.