Another question - do all these 3 spokes sit behind the same NAT device or different ones?
There is a small chance that the NAT entry on the NAT-ing box expired. So, when P2 gets renegotiated, it would PAT to a different port that might cause this issue. You can turn ON DPD or Heartbeat to keep the IKE session active on the NAT-ing device.
It is a fairly long shot, but worth considering 