Your last reply triggered something in my mind.
I once had an issue with Salesforce Commerce Cloud, where I got the same status 500 error.
For better understanding the usecase:
Customer gives us an order reference via contact form and a Freshdesk app tries to fetch that order from Salesforce on ticket creation.
Now not every customer gets the order number correct - Which leads to a 404 response from Salesforce. So far so good.
Now the issue:
Within the 404 response some header was set to a value, Freshdesk was not able to process (I think it was the content type). That lead to that same status 500 error you are experiencing.
So it may be the response from Jira, that the Freshworks part is not able to understand.
In my case, I was fine with the error by assuming/hoping that every status 500 response is in fact a 404.
I am not sure, but I think I found out what the issue was when testing the app in debug mode, because it said exactly which part it could not process. Not sure, but you could try. You would need to connect to a Jira instance, where the issue occurs - Don’t know if one of your customers would give you that information.