More of a note incase anyone else has this issue or if there is a fix for the issue.
I switch the search engine from MYSQL to Elasticsearch with prompted me to reindex catalog search. After running the php72 bin/magento indexer:reindex command the catalog search was returning an unknown error whilst the search engine was set to Elasticsearch and Elasticsearch 5. Switching back to MYSQL and running the command again solved the indexing prompt.
No idea if this is a bug or not.
