Clients not getting DHCP on certain AP

[dragos_dimitriu]

Hi all,

We curretly have a setup with 120 AP's R310 being managed by a SZ100. Network is divided into subnets ,each subnet having a different DHCP pool and VLAN.
On one particular subnet ( comprised of 24 AP) I have a strange problem with one of the AP's in the sense that clients associated to the AP cannot get an IP address from the DHCP 
While troubleshooting the problem with the Troubleshot tool inside SZ we have seen that client correctly authenticates and associates with that articular AP and starts sending DHCP Discover messages but gets no answer from the DHCP server.

Other notes
SZ100, fimware version 3.6.1.0.227 
All other AP's and clients within that subnet work flawlessly ( all clients getting IP addresses from the DHCP server)
DHCP server has still enough leases
SNR and RSSI for clients look ok 
That specific AP is also flagged with 'Connection failures' main reason being DHCP 

Can someone give a hint where to go on with teh investigation ?

Regards