The earliest instance of this issue is on 20160907214111.

@matmarex: Could you provide a little more information? Which browser were you using? Was there a specific page on Commons that you were looking at?

@phuedx You can see the user-agents logged by running the following query on stat1003 (46 result rows):

use log;
select * from UploadWizardExceptionFlowEvent_11772722
where event_message like '%skins.minerva.scripts.top/mainMenu%';

These will all be from Special:UploadWizard, although I saw it on some other page too (don't remember now, sorry). Of course we don't log errors on pages other than Special:UploadWizard in UploadWizard error logs :)

But actually, whatever this was, it seems to be fixed… the latest timestamp in the logs is 20160920144105. The timing seems to match T146099, perhaps it is somehow related?

Change 312946 had a related patch set uploaded (by Jdlrobson):
Be explicit with dependency

https://gerrit.wikimedia.org/r/312946

BTW the current version of the resource-modules linter, although imperfect, is catching some weirdness with the dependencies here (full log):

Error: Dependency problems in file: resources/skins.minerva.scripts/preInit.js:
  ...
  Required skins.minerva.scripts.top/mainMenu defined in file resources/skins.minerva.scripts.top/init.js not found in any ResourceModules

There's more work to be done but I'm hopeful this kind of errors won't slip into master again once we've polished it.

Change 312946 merged by jenkins-bot:
Be explicit with dependency

https://gerrit.wikimedia.org/r/312946

@Jdlrobson - noticed you took this out of the sprint - isn't it done?