Thank you Matias.   To troubleshoot deeper you can capture packets, with the following capture you can see what packets are drop in ASP.   capture CAP type asp-drop   show capture CAP   2: 10:55:09.590957 802.1Q vlan#3604 P6 arp reply 192.168.236.85 ...

I had the same isse.   Disabling icmp inspect fixed me issue.   You can disable it with flexconfig:   policy-map global_policy class inspection_default  no inspect ftp

Hi Stewart,Clustering is supported for Firepower 4100/9300 chassis.Refer to the following link:Deploy a Cluster for Firepower Threat Defense - CiscoRegards,Oscar