mailfilterd stuck at ~100% CPU

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mailfilterd stuck at ~100% CPU, FortiMail 8.0.0 build 183 — cause unclear

FortiMail 8.0.0 build 183. mailfilterd sits at ~99.8% CPU continuously (not a spike), RSS grown to ~1.5GB (baseline is usually ~100MB). All other processes idle. Session count (24–50) and bandwidth are normal, so it's not a traffic flood.

Enabled diagnose debug application mailfilterd level 8 + duration 30 and pulled the Trace Log. The only thing logged for 10 minutes was:

FmailAIClient.cpp:931:ping():entry

repeating once a minute, on a single thread, with no other activity captured — looks like a routine heartbeat, not the actual hot path.

I can't figure out what's actually causing the 100% CPU. Any help would be appreciated.