Several of our users are unable to access the internet when connecting to one of the SSIDs. I increased the DHCP scope a few weeks ago and there a plenty of leases left. I can't explain why this is happening. I'm clutching at straws at the moment - we have about 15 more people in the office than we had last week so in my mind it must be because of this.
I would confirm each AP is working correctly, you'll need to check each port that every AP is connected to, in order to confirm each port is correctly configured. Its possible one port doesn't have a VLAN allowed or something strange like that, which would be preventing 'some' clients from working and other not.
Take a peek at the wireless health tab, do you see anything there standing out?
Check the change log. Check DNS settings on the client/DHCP scope and getting applied correctly. Check L3 rules blocking by IP range than possibly need to be increased when you increased the DHCP scope.