When a setFCV downgrade operation is called on a sharded cluster with viewless timeseries, there is a potential race condition between the setFCV and concurrent DDL operations.
The race condition exists between the time when the function collects the list of namespaces and the actual loop which consumes them.

It is possible for a timeseries collection to be dropped between the two points and be recreated as a view.

If this is the case, a CommandNotSupportedOnView will be thrown. The exception is not among the expected ones, and so the command fails.