Problem DHCP slow 5 minutes strange

[Alexandre85]

Hello, 
I put my problem here, and hope someone could give me some ideas to resolve this. 

On our network, we use Wyse light client, and for some stanges reasons, on a few posts ( we got something like 300 Wyse) there is a problem during boot, to get IP adress from DHCP server. This problem concern something like 20 Wyse, everywhere in the park, and connected to differents switchs. 

The problem, after analyse traffic with wireshark is that Discover message reach the DHCP server without packet loss, the WDM server answer by a offer message but the DHCP server don't. After around 5 minuts, the Wyse show a message, that inform about the problem to reach the DHCP server, and when we close that message, the DHCP server directly answer to DHCP discover message. I have compared the brut UDP stream before the sucess and after, there is no difference at all. 
So i have added a switch after the problematic outlet, and the connexion work perfectly well imediately. 
After that, i decided to plug my wyse directly on the switch, and the connexion work perfectly too, i have also checked my cross connexion cable, and it seems that the problem is due to the cable that connect our outlet.

But it's strange because this problem is everywhere in the compagny building, and the wyse can comunicate perfectly well with the DHCP server after 5 minutes. (the DHCP message directly reach the server when the device is switched on) 

If someone got an idea, anything, don't hesitate to share ;)

Thank's

Alexandre