Random freezing!

Description of setup: We are currently using a total of 8 x different lattepanda sigma PCs in their aluminium case with SSD. The PCs are connected to UPS power source (clean power). There is no monitor connected on HDMI.  The PCs are used for storing and forwarding video from local cameras using Milestone OS. The ambient temperature of the room the PCs are operating in is between 30-40C max. PCs are running windows OS 11 with latest updates.

 

Problem

 

The problem we are experiencing is that on all 8x PCs we see random freezing of the PCs with no pattern.  When I say freeze, I mean the PC is not pingable through network interface - no response to pings, and when connecting a monitor the screen is black.

 

When rebooting the PC, it comes back online, boots into windows, is pingable.

 

Please advise what maybe causing this issue. we installed, thermal pads on SSDs so we dont suspect SSD overheat issue.

 

Thanks.