We've monitored the behavior over the weekend to confirm the issue is resolved. Query Builder is loading as expected since the fix was implemented, on Friday, November 20.
Nov 23, 05:39 EST
We identified an issue with the Query Builder feature. We have already applied a fix, which resolved it.
The Query Builder was either loading very long (50+ sec) or didn't load and returned an error.
When the Query Builder page was opened, and a Data Source selected it took longer time to load. On the next step, when the Metric dropdown was clicked, a timeout message was returned and Metrics in the dropdown not displayed.
All users who were editing Custom Queries were affected.
Nov 20, 08:28 EST