Since you already replaced the cable and it's still happening twice a week — I'd look beyond the cable itself. Two things we found on a similar intermittent 445:
1. The FSSB optical connectors on the amplifier side had micro-contamination. Not visible to the naked eye. We bought a fiber inspection scope (about $150 on Amazon) and found dust particles on 2 of the 4 connectors. Cleaned with IPA and lint-free wipes, alarm frequency dropped from twice a week to zero. Now we clean them during every quarterly PM.
2. Check if the alarm correlates with specific operations on the press. Ours only happened during high-decel moves (fast return stroke). Turned out the regen current was causing enough EMI to momentarily disrupt the FSSB signal. Adding a ferrite core on the FSSB cable near the amplifier end fixed it. Fanuc doesn't mention this in the manual but their field engineer knew about it immediately.
Also — log the exact alarm sub-code. 445 has different detail codes that tell you which node on the FSSB bus dropped. If it's always the same node, the problem is local to that amplifier. If it rotates between nodes, it's more likely a master board or power supply issue.