In case when the GH issue's description is too long, the issue is not being synced to JIRA.
This is due to the fact that JIRA limits the description, example error message:
ERRO Error creating issue for #197. Error: creating Jira issue: reading error body: {"errorMessages":[],"errors":{"description":"The entered text is too long. It exceeds the allowed limit of 32,767 characters."}}