Can you describe how do you confirm the firewall is unable to resolve the domains? Have you checked it from the GUI or CLI of firewall?
Mostly, the reason for the firewall not able to resolve the FQDNs is due to the firewall unable to reach the DNS server.
By default, mgmt interface is used to connect to the DNS server (but can be changed from Device > Setup > Services > Service Route Configuration)
You can check if the DNS server is reachable. The CLI command below can then be used to view the list of FQDN objects and the IP addresses associated with that name.
Alternatively, you can also check the FQDN resolution on the GUI by navigating to Address Objects > Select the FQDN Address Object in question > Click on 'resolve'.
Please go through the below KBs, which can be of help:
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