Description of the problem:

Intermittently the kafka script will fail with 
kafka\nerror: resource mapping not found for name: \"my-cluster\" namespace:
How reproducible:

50%

I am fairly certain the problem is just timing related. When 

oc create -f 'https://strimzi.io/install/latest?namespace=kafka' -n kafka

is run it creates a significant of CRDs and other resources. The next line is  

 oc apply -f https://strimzi.io/examples/latest/kafka/kafka-single-node.yaml -n kafka 

which references the CRDs - in some cases the CRDs may not be created by the time they are referenced and the script fails.