ipsec tunnel fails

Hello.

I have several SRX boxes with RB IPsec VPNs at it.

one of the box have a trouble - only one tunnel suddenly drops (3 other tunnels work fine).

here is output

root@problem_srx> show security ipsec inactive-tunnels
Total inactive tunnels: 1
Total inactive tunnels with establish immediately: 1
ID Port Nego# Fail# Flag Gateway Tunnel Down Reason
131076 500 112 0 600a29 178.236.xxx.xxx Peer Entry cleanup

other side:

root@srx> show security ipsec inactive-tunnels
  Total inactive tunnels: 1
  Total inactive tunnels with establish immediately: 1
  ID     Port  Nego#  Fail#  Flag      Gateway          Tunnel Down Reason
  131100 500   114    0      600a29    95.54.xx.xx      VPN monitoring

what does "Peer Entry cleanup" means?

how to find the root cause of this?

I've tried to change problem SRX to another one, updated FW (it's Model: srx100h2 JUNOS Software Release [12.1X47-D20.7] now).

both boxes have several tunnels, but only one drops.

any ideas?

thanks.