I recently went to update (manually) to 3.1.1 from 2.something. Experienced odd issues with not being able to export survey responses, and getting logged out all the time. Almost after every click in the UI. At least when trying to interact with a survey.
I eventually removed the DB and installation on my server and did a fresh install of v 3.1.1. Can't speak for the issues regarding exporting survey responses, but the issue with getting logged out remains. For example, want to preview a survey. By the time the link in the new tab opens up, I've been logged out in the main tab and can't preview the survey (get the error page about permissions).
Cleared cookies and cache in my web browsers used for testing (Chrome and Safari). Back-end DB is MySQL, running PHP7.
I've done several installations of LimeSurvey over the years, so I don't think I've missed something in the installation process, so this should possibly be submitted to the bug tracker. However, as it's not a subtle issue, I would have thought it would have been picked up beforehand, so there may be something odd going on here for me.
I noticed version 3.4.0 was available, so I've tried a clean install of that.
Still the same issue. Perhaps worth noting that it seems specifically when engaging with a survey. When I have gone into navigating general settings - no trouble..
I create a new survey, give it a title, an end URL and set the date format, I could save it. When I went to "structure" and wanted to "add a new question group", I get booted out. And then after every single operation I try to do it seems.