We had/have an issue with windows 8/8.1; It sounds similar to yours, on our 802.1x network eduroam users were connecting and then dropping and having difficulty getting online. A symptom was that they were often asked to re-enter credentials.
The solution was to DISABLE 'Enable Pairwise Master Key (PMK) caching.
This is found in the wlan network properties, security tab, advanced settings, new window 802.11 settings.