PF-Sense NAT Translation with IP poll Network address/Broadcast address problem

[vamsi]

All
I do not know any one having this problem.

My Pfsense box was configured for NAT with Round robin with an ip pool of 111.xxx.xxx.121/29.

Problem we are facing is, when Pfsense picks up Network address ie 111.xxx.xxx.120 for NAT, one of our VPS will losing connection/pack drops happens(it will respond but very slow). IF I do 1-1 NAT (with proper address), there is no problem.

With out 1-1 NAT, if Pfsense picks up other than network address or broadcast address works fine.
All other servers well behave in this scenario (with broadcast address/ Network address) other than the said VPS.

I have no clue what is happening, and is this datacenter firewall problem where we are hosting?

Please help

Thanks
Vamsi