By default, the JRE will cache DNS settings and info. The default is 30 seconds of caching, and during that time, if your Load Balancer uses many unique IP addresses, they all might not be used.
There is a way to limit the value for caching DNS, but it is to be used with real caution, as it can have severe consequences to your network, and could lead to vulnerabilities to DNS Spoofing attacks.
Here is an excerpt from the config file (neoload-install-dir\jre\lib\security\java.security property file):
The Java-level namelookup cache policy for successful lookups:
any negative value: caching forever
any positive value: the number of seconds to cache an address for
zero: do not cache
The default value is forever (FOREVER). For security reasons, this
caching is made forever when a security manager is set. When a security
manager is not set, the default behavior in this implementation
is to cache for 30 seconds.
NOTE: setting this to anything other than the default value can have
serious security implications. Do not set it unless
you are sure you are not exposed to DNS spoofing attack.
So, putting the value to zero would tell Neoload not to cache the DNS, and try to grab a new IP from the LOad Balancer. Be careful with this, and note you must restart Neoload and/or LG Agent to take effect.