About a month ago I upgraded EE from 2.5.2 to 2.7.2 in my staging environment with absolutely no problems. The upgrade went smoothly and it's been running like buttah.
Last night, I attempted the same upgrade in our production environment following EE's update instructions to the letter. Things were fine until the update wizard ran (step 6 in the instructions). The update wizard would appear to complete its updates, I would remove the "installer" directory from the "system" directory, but then when I'd enter the URL to go to the control panel, the first screen on the update wizard would display instead despite it actually being removed from the server.
Both the staging and production environments are on AWS, but prod is load balanced on two servers, but linked to one database (I think). There's no caching, except using CE Cache.
I'm wondering now if it has to do with both web servers having the control panel on it? Anybody have any ideas?