Hopefully MaxSem will remember about this...
We had a few incidents of gadgets just disappearing on the labs wikis. I can't remember if purge/null edit fixed it (or even a blanking and revert)....
Well, we've just had the (seemingly) same issues reported on enwiki/dewiki - Gadgets tab gone, blank and revert fixed it
[19:39:57] <kaldari> I've been doing action=purge on them, does that work?
[19:40:05] <hoo> kaldari: no, tested it before
[19:40:13] <kaldari> :(
^ So purge didn't fix it, I'm guessing nulledit fixed it...
It seems to be some sort of cache related fail/error handling