How to understand what is happening with cisco (*crashdump is empty*... because of which it rebooted)?

Question

System administration

Help to understand pliz.
today one of the Catalyst 4500 central switches rebooted for no

apparent reason, if in a nutshell, the structure is as follows:
two central Catalyst 4500 switches to them three stacks of three ciss in each C2960S (they have ports written like this:
!
interface GigabitEthernet1/0/5
switchport access vlan 10
switchport mode access
switchport voice vlan 40
spanning-tree portfast
spanning-tree bpduguard enable
!

from each stack goes through 10Gbit optics to cisco4500 (in both)
4500 catalysts themselves 10Gbit optics

stood everything worked and how it started this morning Problems.
I go to the first catalyst (which rebooted, I watch the crashdump, and there it is from the 23rd.)

RT01-1#sh platform crashdump 
Last Power Failure: 01/23/2020 21:54:24

Crash file: crashinfo:crashinfo_eicored_20200227-122524-UTC
====== signr 11

======= Process

PID=8695   PPPID=1   PGRP=5705
Time: User=1225   System=402

======= current - pid 8695

====== Registers

nip = 0x48A59A80  msr = 0x0002D000  r3* = 0x00000018 ctr =  0x00000004
lnk = 0x486FE724  xer = 0x20000000  ccr = 0x48444442
trp = 0x00000300  dar = 0x00000000  isr = 0x00000000  res =  0x00000000
R0  0x00000000  R1  0x53A0FA60  R2  0x53A17930  R3  0x00000000
R4  0x00000004  R5  0x5E11E958  R6  0x000F4240  R7  0x00000018

RT01-1 uptime is 4 hours, 8 minutes
System returned to ROM by reload
System restarted at 12:29:07 IRKUTSK Thu Feb 27 2020
Running default software
Jawa Revision 7, Snowtrooper Revision 0x0.0x1C

Last reload reason: Unknown reason

or anything interesting ...
where to look how to understand what happened?

ps everything worked for 5 years.