BIG-IP 17.1.2 FastL4 unexpectedly sending TCP RST mid-session

Hi everyone,

I am troubleshooting unexpected TCP RST packets physically sent by a BIG-IP 17.1.2 Performance L4 virtual server using the default FastL4 profile.

The virtual server performs SNAT and forwards traffic through a single next-hop pool member (the default gateway), so there is no load balancing across multiple servers. There are no traffic policies, iRules, AFM, ASM, or HA/mirroring configured.

TCP connections establish successfully, complete TLS, and exchange application data. After that, BIG-IP sends TCP RST packets and terminates the established session. Packet captures suggest that the resets do not appear to be caused by the configured idle timeout.

Has anyone seen similar behavior with FastL4 on TMOS 17.1.2, or knows of a configuration, FastL4/TMM behavior, or known issue that could generate RST packets mid-session?

Thanks in advance.