I cannot delete an issue due to indexing failures

[George Tsatsis]

My JIRA instance bugged out and made a subtask a task, and now I am unable to delete said issue to re-make it (I cannot change it's details either):
Error: 

The error can be found at https://pastebin.com/1MPMKP3Y

[Andy Heinzer]

I would recommend trying to follow the steps in the KB Unable to rebuild JIRA application indexes

1. Stop JIRA

2. Make a backup of the following directory and all its sub-directories:

   $JIRA_HOME/caches/indexes

3. Remove that directory and all its sub-directories:

   $JIRA_HOME/caches/indexes

    This will be rebuilt when JIRA is re-indexed

4. Start JIRA
5. Perform a locked/full re-index of JIRA

If you are still seeing errors when Jira tries to reindex this data, I would be interested to see what details exist within the stacktrace.

Andy