Upgrade to firmware 6.42.09.0005 or higher.Release notes
state, in the 'Firmware Changes and Enhancements' section:
15297 Addressed an issue associated with the switch port state machine which could potentially cause device ports to lockup.
Latest firmware and release notes can be found at:https://extranet.extremenetworks.com/downloads/Pages/B5.aspx
Pre-upgrade workaround: The switch after a manual reset works fine for some time.