Strange SSD boot failure

I have a Windows 10 Pro system, build 19045.3930, with following specs:
ASRock X570 Steel Legend motherboard
Ryzen 7 5800X3D
32GB DRAM, DDR4-3200
NVidia RTX 2080Ti GPU
2TB m.2 Gen4 SSD (boot, on motherboard)
4TB m.2 Gen3 SSD (bulk storage, on PCIe3 addon card)
4TB m.2 Gen4 SSD (games, on motherboard)
1000W power supply

All had been running fine over past year or so.
However, I'd been having occasions where I was running short of memory (yes, even with 32GB)...
I tend to leave email and multiple browsers open all the time, along with various other programs, and they tend to tie up memory after awhile... so I decided to upgrade two of my DIMMs to 16GB from 8GB, giving me 48GB total...
I got the same species of DRAM for the upgrade, as I had on the originals, Corsair DDR4-3200 ...
I carefully installed the two new DIMMs in alternating slots, as instructed in the motherboard manual...
I then booted into the BIOS, and it said the memory modules were all properly installed...

but... when I went to boot the computer, it said the boot drive was not readable...
I looked in the BIOS, at boot-drive selection, and my 2TB boot drive was not in the list...
I tried switching back to the original DIMMs (though I don't see how DRAM could be involved in this??), but that made no difference...

I considered unplugging and replugging the SSD modules, but on the ASRock motherboard, they are inaccessible under a plate.

Anyway, I took the system to Central Computer, Newark, CA, USA, who have done good support work for me before.
The tech there booted my system to Ventoy to look at things, and it reported that the boot sector was corrupted.
He used Ventoy to rebuild the boot sector, and then everything booted, and is working fine, and my 48GB of RAM is working fine as well...

but I don't have any idea what swapping memory modules had to do with my SSD drives, which aren't even accessible under that plate... Does anyone have any idea what happened here?? Is this something that typically happens with m.2 boot drives when upgrading memory??

The one thing I've seen in years past [30] of building and repairing computers is that the ATX motherboards always have power to the when off, only way to prevent damage was to remove the power source, press the power switch so as to drain any residual power before making any hardware changes. The power supply connects to the motherboard and the motherboard connects to the switch, the switch tells the board to get things going. When I first started the AT boards connected to the power supply and the switch connected to the power supply to turn it on. And safe computing dictates discharging static from one's self before touching the internals.