Id look at another reason beyond SoapUI for a reason your balancing isnt following expected behaviour.
SoapUI only caches at projectlevel and this is just the caching of wsdls, wadls, openAPI/swagger files.
How are your endpoints redundancy handled in your balanced architecture? if your wsdl, wadl, openapi/swagger files have single endpoints defined, then surely this would bypass any load balancing and your single endpoint would receive all the hits rather than a percentage, right? Or am I missing something?
if this helped answer the post, could you please mark it as 'solved'? Also if you consider whether the title of your post is relevant? Perhaps if the post is solved, it might make sense to update the Subject header field of the post to something more descriptive? This will help people when searching for problems. Ta