Weird behavior after HDD replacement

Hi !

To keep it short, I got a 5G AP Time Capsule for several years now. Until recently the TC was working like a charm with the original 2To Seagate HDD.

I bought first a 12TB HDD (Seagate Exos X16) to replace the 2TB that was on the TC. I have tested the disk before mounting it on Windows (CrystalDiskInfo) and also on MacOS (DriveDX/Disk Utility/Disk Drill Disk Tool). All seems to be clear. I have done it several time because of the noise that was weird to me (but it has been a while since I din't heard a HDD scratching).

Well, the mounting was done smoothly and the configuration also. Btw I configured it as follow :
- Static Internet connexion with assign IP
- Wireless OFF, I don't need it
- Network mode is bridge
- Extra details : TC is plugged with c5e ethernet cable and I am using Catalin (10.15.7)

Now, the issue... Its driving me crazy because I can't manage to isolate the cause. Everything seems to work "just fine" (LED is full green) but when I am launching the first save (~550Go), the TC is rebooting randomly. It could happen around 100Go or at the beginning. So since few days, I wasn't able to complete the first save.
The weirdest thing, and this is where I am totally lost, is than every time the TC is rebooting, is making my router reboot aswell... So I am loosing WAN in top of that. How is that possible ? Like if it was the opposite of magic packet...

Here is what I have tried so far :
- Factory reset several time the TC . Turning the Wifi On, DHCP Internet. Erasing the disk. Doing it only with a ethernet cable between my MBPro and the TC. Résultat = NOK. Same issue.

Here is what I am going to try :
- Putting back the original disk to see if the issue is still happening. If yes, I am going to send back the drive.

If anyone has already encounter this issue and know any details about that, it will be appreciated. Thank you very much for your help.