Sometimes Magento Admin will stop working. It just tries and tries to connect. If I load it up in a new browser it works again immediately. This is happening in different browsers (I mainly use chrome). Even if I close the tab, and try and load it again in a new tab it doesn't work. As soon as I load up "incognito mode" it works. This happens so often that it's really annoying. Any ideas?
This is an artifact of session locking when using filesystem-based sessions. To avoid this it is recommended that you instead use Memcache or Redis. This question has been asked before and is better answered by @blackbooker:
A write lock is being placed on the session data file when it is opened by the initial (long-running) request, causing the second request to block until the lock is released when it calls session_start in Mage_Core_Model_Session_Abstract_Varien::start