Hi
This is an issue I am experiencing on Persian Wikipedia (FAWP) for the last couple of weeks. I have replicated it in different machines, and after clearing the cache (or using incognito). I have replicated it in Firefox and in Chrome.
When you open a page, some times certain widgets (e.g. Twinkle) or user-specific JS scripts don't load. Refreshing the page will fix it 99% of the time (that 1% requires refreshing 2 or 3 times).
Looking at the console shows an error that indicates "mw.util" is not defined. See the error message in Firefox[1] and Chrome[2] But because none of the scripts have changed recently, to me it means somehow that mw.util is not loaded *some of the time*.
The problem manifests itself mostly when you open a tab in the background (i.e. you middle-click a link), and especially when I open several tabs in the background.
If I turn ResourceLoader off, the error does not occur. So I am thinking it has to do with RL. Any ideas on the next steps to investigate this are appreciated.
Huji
[1] https://commons.wikimedia.org/wiki/File:Firefox-mw.util-error.png [2] https://commons.wikimedia.org/wiki/File:Chrome-mw.util-error.png