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