Cisco Aironet 1815I Mobility Express Multiple SSID not working

Hello

I want to have two SSID for our network, one for our users and one for our guests. I've setup so that one AP is for users VLAN and one is for guests VLAN on the switch running on trunk ports. I also put each AP in their own AP Group in the GUI so that the APs will only broadcast their own SSIDs.

Here is where I am experiencing problems, with one SSID I can connect and get an address no problem. But when I create the next SSID for our guests, sometimes I can connect to it and wont get an address and sometimes I get an address and sometimes I cant connect to that specific SSID. After a reboot of that AP I could however connect but why does this problem occur and how do I fix it

I have two Cisco Aironet 1815I APs connected to a 2960 switch. Running the latest version available from Cisco.