See Tip: Troubleshooting Client Reponsiveness for my detailed post on troubleshooting. From your description it sounds very likely that UDP from the Relay to the Client is being blocked, possibly by the Red Hat firewall.
From the BES Support site, check whether this Task is relevant, you could run that to add an exception to for BigFix traffic on firewalld:
678 RedHat Firewall is Blocking BES Traffic - BES Client
If it’s not relevant, I’d check anyway into the firewall configuration; this check in Relevance can be tricky depending on your mix of ipchains, iptables, firewalld, or third-party EDR products.