If the question is about Clients already registered and reporting into your new BigFix Server, it sounds like you may need to troubleshoot Client responsiveness. Jason has a good topic on this:
If my guess is correct, I’d suggest reviewing the following section from the topic above: “If the client is posting reports, but much less frequently than expected; is receiving GatherHashMV messages, but is slow to execute or report back Analysis results, there may be long-running evaluations”
Regardless, I’d suggest opening a Support case to help troubleshoot further.