"Zombie" job items are left unfinished in the queue if translation doesn't complete

Problem/Motivation

I have two sites that run continuous translation jobs using this module and they all accrue a long list of job items that are in various stages of translation and are not resumed on cron run. Newly added jobs are translated when cron runs, but if they don't complete, they're left unfinished and won't be resumed.

Steps to reproduce

Create a large batch of translations and interrupt the process. Or run continuous jobs and submit a few nodes. The "Job items" UI will start showing partially finished jobs like the attached screenshots.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes