Error "Something went wrong" when using "New pull request experience" Labs feature

Issue Summary

A "Something went wrong" error appears in UI with the "New pull request experience" Labs feature enabled if the pull request difference is very large, so that it's processing time is very close to timeout thresholds. The PR might sometimes load and other times not, depending on the time of day (load on the server), local network conditions, or other factors. The network interactions for the page show a 555 response code for the PR diff request.

Steps to Reproduce

1. View a large Pull Request with "New pull request experience" Labs feature enabled.
2. "Something went wrong" may appear depending on size of PR diff, network conditions, and time of day.

Expected Results

Pull request should display the diff between branches of the PR.

Actual Results

Error message "Something went wrong" in UI with new pull request experience, and 555 response code in Network tab.

Workaround

Review the PR using the old pull request experience.

To return to the old pull request experience for all PRs:

1. Click on your avatar icon in the lower left corner of any Bitbucket page.
2. Select Bitbucket Labs.
3. Disable "New Pull request experience" feature.
4. Enable "Old Pull request experience" feature.

If Old PR has some issue, Please review the PR locally using git diff command and merge either locally or through UI.