In your VIP configuration, try to specify your WAN IP considered, as a /24 and not a /32.
For instance…
Let say your ISP gave you this set of IPs :
193.204.32.1, .2, .3, .4
Let say you want your web site on the 193.204.32.3.
In your VIP configuration, spercify the VIP IP as 193.204.32.3, but force it on /24 mask (not a /32).