External Task is INTERNALLY_TERMINATED but does execute

We have a Camunda external task (on bpm platform version 7.14) that is not executing (none of the logging inside the external task is output) yet that task causes the entire process instance to be INTERNALLY_TERMINATED. So far, have found no error messages in the logs.

Are there any limitations on the number of variables that can be used ? Wondering if some limitation is being hit that is causing this problem.

Any help or ideas would be appreciated.