@alemabrahao    Its now sorted ,  it looked like some of the  " Firewall & traffic shaping " rules for the relevant site were preventing clients traffic to get to the DNS Server .   Thanks All for your help    ... View more

So you had tagged the VLAN on the AP, now it makes sense, if it had not been tagged the AP would receive the IP of the native VLAN (not tagged), maybe you missed informing this detail. ... View more

Hi All   Just to let you know  the matter is now solved . Our on Prem Firewall had a Zone protection profile  with a setting instructing  the firewall to drop fragmented traffic . Once  that setting was updated it worked .   Thanks all for your contributions ... View more