I have one web server where we have a staging instance and a live instance running at the same time. Up until recently, we have been able to stay logged into both at the same time. We have only made a few minor changes recently:
We changed the maximum cookie lifetime from one hour to one day - I undid this and the problem still exists.
We changed the php memory limit to import some products as the import would fail due to out of memory error, but that was changed back after the import was done.
we added a third instance for development, but I don't see how that could be causing problems (could it?)
The problem is, now, when logged into the admin panel in live or staging or dev, logging into the admin on one of the other instances causes us to have to re-login to the one we were previously logged into. What would cause this behavior to suddenly happen after we had no problems for years?