motherboard will not boot after hibernation overnight (on 2nd RMA)

[skyfishgoo]

i'm at a complete loss after 2nd RMA
suspend and resume work fine in the daytime during testing, but overnight the motherboard dies and eventually cannot be revived.
what i've tried:

• cleared CMOS
• reseating all power connections
• tested PSU voltages (paper clip test)
• tried to flash the BIOS (will not accept flash)
• tried alternate CMOS (via dip switch)
• tried to flash BIOS again to alt CMOS
• removed network connection
• removed power cable and let is sit for hours at a time
• removed m/b from case and flashed BIOS without cpu or ram
• RMA original m/b twice and got back a different (older) s/n on the 2nd RMA

at first performance seems good, boots fine, all h/w is recognized by firmware, OS suspends and resumes as expected from both S3 (suspend to RAM) and S4 (suspend to disk) with all my firmware settings in place.
but if i leave it overnight in S4 one too many times, it will not boot the next mornging and will not accept a flash on either CMOS... this has now happened to two separate s/n of the same motherboard model
what? why? wtf is going on here?
system:

• MSI MEG ACE z690 motherboard with latest firmware (rev J)
• i7-14700k CPU
• RX 6800 GPU
• ADATA 2x32GB Lancer RAM (QVL listed)
• lian li GA TRINITY II PERFORMANCE 360 AIO
• be quiet Dark Power 13 1000W PSU
• OS kubuntu 24.10

btw it seems to work fine with windows 10 but i've not tried leaving it overnight suspended in windows because i rarely use windows.

[skyfishgoo]

leaving it unplugged for several hours seems to allow it to be re-flashed (so far) but this is what i ran into on the first RMA... eventually if won't even take a re-flash.

my working theory is there is some process or timer that wakes up the machine in the middle of the night and runs it into a wall, so by the time i find it in the morning it's brain dead.

anyone have any ideas what could be running at 2AM to cause this?

started looking into

https://linuxcapable.com/how-to-conf...-ubuntu-linux/

but that seems to be for servers which run all the time and never hibernate, so not sure how it could wake up a sleeping system.