HP Dl380 Gen7 random reboots

Hello. 

Have random reboot (period 2-60 days) problem with 3 from 3 HP DL380 Gen7 servers in one datacenter. Have a server of other manufacturer near HP servers and it works stable.

All servers have 2 power supplies and in logs (ipitool sel list) i see only messages about power failure on one of supplies:

a | 09/30/2017 | 14:45:48 | Power Supply #0x04 | Failure detected | Asserted
b | 02/11/2018 | 10:41:59 | Power Supply #0x04 | Failure detected | Asserted

sdr -v shows active power redundancy :

Sensor ID              : Power Supplies (0x5)
 Entity ID             : 10.3 (Power Supply)
 Sensor Type (Discrete): Power Supply (0x08)
 Sensor Reading        : 0h
 Event Message Control : Entire Sensor Only
 States Asserted       : Redundancy State
                         [Fully Redundant]
 Assertions Enabled    : Redundancy State
                         [Non-Redundant: Sufficient from Redundant]
                         [Non-Redundant: Sufficient from Insufficient]
                         [Non-Redundant: Insufficient Resources]
 Deassertions Enabled  : Redundancy State
                         [Redundancy Lost]
 OEM                   : 0

Why I see a reboot if only one power supply fails?