Jira is unable to parse custom timezone and causing Internal Server Error in classic boards

Issue Summary

Jira uses a library to parse the timezone of a user and calculate the remaining working days of a sprint. The library was unable to parse a user entered timezone correctly and throwing a status code 500 for board loads.

Steps to Reproduce

1. Go to account settings
2. Select Account Preference
3. Change your timezone to a custom timezone(ex GMT+3:00). (Do not use the timezones in drop down as they work fine)

Expected Results

The classic boards should load without error. 

Actual Results

The board is throwing a status code 500 while loading.

Workaround

 The workaround is for users to change the timezone to a standard one in their Atlassian account settings.