504 Gateway Timeouts when mousing over after the page has loaded for a while

Created by: lawrence-tan

• Sourcegraph version: 3.18.0
• Platform information: Firefox 79.0 on macOS 10.15.5

Steps to reproduce:

1. Load a source file in Sourcegraph, and mouse over an element to get a code intelligence popup.
2. Move your mouse away to dismiss the popup.
3. Leave the page alone for 5 minutes.
4. Go back to the page and mouse over another element.

Expected behavior:

A code intelligence popup appears.

Actual behavior:

Nothing happens. Errors show up in the console, and I've attached a screenshot of one set of errors.