SmartView Tracker logs show that IPS protection "TCP Off-Path Sequence Inference" drops TCP packets originated by Security Gateway:
Blade: IPS Action: Drop Attack Name: Streaming Engine: TCP off-path sequence inference Attack Information: TCP off-path sequence inference. Protection Name: TCP off-path sequence inference Protection ID: tcp_off_path_enable
SecureXL status (enabled / disabled) is not relevant.
IPS protection "TCP Off-Path Sequence Inference" drops TCP packets originated by Security Gateway that contain "ACK" number that was already accepted.