9720 : wifi problem
No sure ideas. If it were me, I would try the following...
Delete the wifi profiles on the device. Reset the device by removing the battery while power is on. Recreate the profiles and test.
And if that isn't the fix, do a backup and a security wipe. Do not restore settings and app data, just personal data like calendar and contacts. Test.
And if the problem remains, do a clean OS install. Again, do not restore settings and app data. Test.