2017 iMac 27" Random Sudden Shutdowns

Spec and condition:

iMac 2017 5K, CPU: 4.2GHz quad-core 7th-generation Intel Corei7, RAM: 32GB 2400MHz DDR4

Graphic: Radeon-pro 580 8GB Video memory, HDD: 2TB Fusion, OS 10.14.2(Mojave)

AppleCare till 2020

Using Apple Magic Trackpad2 and Apple keyboard with numeric keypad, connected to the internet via Wireless directly to the modem (no WiFi extender).

No other device is attached. The iMac is 5 feet away from any wall (proper ventilation) and room Temp around 74 F (23C).

Issue:

Sudden Shutdowns with no specific pattern! Won't Turn on after that, unless unplug it and plug it back again (Reseting SMC).

It was fine since Aug 2017 till 28 Sep 2018 when it got started.

It can happen while doing different tasks (Browsing one tab! typing in the Note, or writing (not running) python code, ...)

There will be no kernel panic or crash report in console after the incident!

The first day it happened 12 times in 24 hours!

last month I changed the setting to wake up after power failure and it did not change anything.

What I tried:

Different outlets, different rooms with separate fuses (no change, it happened again).

Bypassing the surge protector that was in use before and connect directly to the wall (no change, it happened again).

Formatting all partitions and reinstalling new OS on one partition. (no change, it happened again).

Reseting NVRAM (no change, it happened again).

Have been to the apple store 4 times and they couldn't figure it out yet. Last time( 2 months ago) they said in one or two days someone from Engineering department will call us to have online access to our logs which hasn't happened yet.

I found a video (iMac ShutdownSuddenlyandRandomly by TheAjmartins) on youtube and in the comment section it seems that other people with iMacs had and still have the same issue. Most people there believe it is related to the power supply unit and changing that solved their problem although some other people still had the issue even after changing the power unit and the logic board. Some say for them it happened right after updating to the new OS (to Sierra or ElCapitan for them) for me it happened 4 days after upgrading to Mojave which might be relevant or not !

It is been 93 days and no one had any idea about what is going on.