Can a CPU "recover"? Or My tale of woe and joy! Ryzen 7 5700G

[wakou222]

Hallo clever people!
I have an intriguing and head-scratching situation, involving a Ryzen 7 5700g, but might apply to other CPU's.
TL: DR?
Brand new CPU/APU, on first installation would spin up and cycle/loop trying to POST, on two different rigs. Eventually posted/booted, and is now fine. How can this be?

So, some weeks ago I was in a old-style bricks-and-mortar auction house, where they had a quantity of brand-new, boxed and sealed Ryzen 7 5700g. I managed to 'win' two of them, for a reasonable price, one for me and one for some benign scalping (to cover my fuel costs, and time etc! Another punter bought the other 10 or so!)
I mentioned these to a young neighbour, and shortly afterwards he told me that a college pal would like one, but was tight for cash until the end of the month, and could I hold it?
Me "Of course! And seeing as you are a friend, he can have it now and pay me when he has the cash".
Two days later, my neighbour calls and says he has managed to find the cash, and can he come and get the item?..
Some days pass, and...
"My friend can't get it to work.. can he have his money back?"
Me "WTF?? It was boxed and sealed! Now it is used, and possibly abused and god only knows what your pal has done to it".
I asked all of the questions you might expect, and a few choice others, for good measure.
My neighbour is young, and a good and trusted friend, so I reluctantly agreed and returned the ££, and got back the CPU.
Yesterday I opened it and gave it a thorough visual inspection with a magnifying glass etc. No signs of abuse, or even of use. No liquid-metal dribbled over the pins, no bent or damaged pins. The bundled cooler was definitely not used, as it still had the factory-applied thermal paste, immaculately intact.
I don't have a bench-rig with spare compatible MoBo, so I reluctantly stripped my own and put the chip in.
The moment of truth arrived and, whirr-whoosh...
And.....
It was cycling as if trying to POST. No error codes or beeps. I don't have a Dr Debug, nor (AFAIK) any error-leds on my mobo. No output to monitor.
And I tried a few times. Fans spin up, settle, HDD initialises.. Then fans spin up, settle etc... in a loop. (I have a vid if this would help)
Hmm! I surmised that perhaps it was somehow pre-set to use the on-board IGP, so I went and found a HDMI cable, and plugged that into the MoBo output. Tried again. And again. Then.... the BIOS/UEFI screen flashed on my monitor... and then it went back to cycling in a loop!
I disconnected the HDMI cable, and reconnected the Display Port to my Graphics card.. Switched on and.......
Guess what? One beep, straight past the UEFI and tries to boot Windows! It would not of course, due to TPM and different CPU etc...
Back in to the UEFI/BIOS, a quick reset, and everything is running beautifully! How can this have happened?

I have:
GigaByte Gaming B550M, BIOS F14e, 2x 8gb Corsair 3600 DDR4, NVidia GTX 1070. All were working perfectly with my previous Ryzen 3 3100

The FoaF, (I am told) "Knows what he is doing":
MSI Mortar MAX B450M, up to date BIOS. He tried with only one stick of RAM etc.
He said the CPU was "getting warm", I asked via my friend, "how did he know, was he running with no cooler and using his finger?" My friend replied that he has a temperature-probe-gun thing.... (?)

 

[wakou222]

I am not sure he did try without a cooler, I am assured that is not the case, and besides, surely he would have put one on PDQ as soon as he noticed an issue?
But even if he did why did the chip take a while to begin working on mine, and has been running perfect since? (I am using it now as my 'main' PC).
I suspected that it was perhaps to do with "Secure Boot" or TPM, or similar settings in the BIOS/UEFI might have been an issue. But I am told that HE flashed his BIOS to bring his MoBo up to date, so those things would not have stopped his rig from POSTing?
Can a CPU somehow "store" a setting? like an overtemp or something?
Can 'secure boot' or TPM stop a new CPU from POSTing at all?

One other, slighty more prosaic theory.
My neighbour (and I presume his friend) are young (17). Could it be perhaps that Mr X used some money given to him for say college fees, driving lessons etc etc, and an angry parent had found out that he had "wasted it on silly computer games and stuff" and ORDERED him to return it and get the money back by whatever means necessary? The embarassment would perhaps explain his reluctance to speak with me directly, or Whats'app etc?
Although, AFAIK, they are both studying Aeronautical Engineering (my neighbour is) and had I been in that position I could have made a clear case that a PC capable of running MS Flight Simulator properly was a very sensible use of money!
And would not explain why the CPU at first refused to play nice in my PC..... And then DID and has been fine ever since?

A mystery!

 

[wakou222]

@Cyber-Mav

Check serial number of cpu matches the box.

This is excellent advice! I did not think of that as possible reason (swapping etc) , but I did check when installing it to mine, and took pics, and they do match.. but thank you!
@CuriousTomCat

If the guy owns an infrared thermometer gun for checking CPU temperatures then he's definitely an enthusiast so probs has an AIO or similar.

Yes, I think he is... But of course, many of us have non-contact thermometers these days, what with the covids etc?