Unexpected reboots, Ubuntu Server

I am trying to find how to check if that is a hardware issue. What tools can I use to figure where is the problem?

It seems the server is running stable when it is not loaded and just sitting idling with a full stack development tools running. Overheating is not the case, temperature is under 40 celsius while loaded at max.

I have a docker installed with librePhotos and running nextcloud in a snap. While the librePhotos was indexing raid media array with around 1.2TB photos and videos the server keeps restarting once in a while. Also tried to use photoprism and the server was doing the same thing when indexing the media drive.

Output from last reboot:

reboot   system boot  5.4.0-96-generic Mon Jan 24 03:44   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 23:16   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 23:01   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 22:48   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 22:35   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 22:22   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 22:08   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 21:55   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 21:39   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 21:24   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 21:08   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 20:49   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 20:26   still running
reboot   system boot  5.4.0-96-generic Sun Jan 23 20:07   still running
reboot   system boot  5.4.0-94-generic Sat Jan 22 01:41   still running
reboot   system boot  5.4.0-94-generic Tue Jan 18 01:29 - 14:06 (1+12:37)

Output from the status of the array:

Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdb[0] sdc[1]
      2930134464 blocks super 1.2 [2/2] [UU]
      bitmap: 0/22 pages [0KB], 65536KB chunk
Server's configuration:
EVGA 600 W3, 80+ White 600W
SUPERMICRO MBD-X9SCL LGA1155 Intel C202 Micro ATX Motherboard
Intel Xeon e3-1220L 3.33Ghz 12MB sr070 LGA1155 dell 1g5m7 HTPC
LSI 9212-4I 6GB/s SATA3 / SAS2 4-port HBA / RAID Controller PCI-E Expansion Card (IT mode)
Raid Array 2x3TB 3.5 Hitachi HUS724030ALS640 SAS 7200RPM 128MB 6GB/s HDD hard drive HGST
Ubuntu 500gb WD SSD

If anyone has an idea how to check before I start disconnecting the hardware, and what to disconnect in order to solve this?