1 Slot Ram Motherboard

See it on Newegg; CPU Socket: LGA1200 Chipset: Z490 Memory Slots: 4 x DDR4 Channel Support: Dual Max Memory Speed: 5,000MHz Max Memory Capacity: 128GB Expansion Slots: 1 x PCIe 3.0 x16; 1 x PCIe 3. GIGABYTE X399 AORUS XTREME sTR4 AMD X399 SATA 6Gb/s USB 3.1 Extended ATX AMD Motherboard. Limited time offer, ends 02/28. Number of Memory Slots: 8×288pin Memory Standard: Support for DDR4 3600+.(O.C.)/ 3466+(O.C.)/ 2933/ 2667/ 2400/ 2133 MHz memory modules. Recommend to use a 1st Gen. Ryzen Threadripper processor to achieve 3600 MHz (O.C.) speed. There are also converter cards, known as Slotkets, which hold a Socket 8 so that a Pentium Pro CPU can be used with Slot 1 motherboards. These specific converters, however, are rare. Another kind of slotket allows using a Socket 370 CPU in a Slot 1. ASRock B450 Gaming-ITX/AC. Chipset: B450 Overclocking Support: Yes SATA Ports: 4 M.2 Slots.

I have been meaning to post this for a while, here goes finally.
I have a lot of system building experience, and generally held the belief that bad RAM slots on motherboards are uncommon. The first one I encountered was a couple of years ago - I opened up a brand new ITX celeron board and I eventually discovered that one of the RAM slots was bad. The motherboard wouldn't boot with any RAM installed in one of the two RAM slots on the motherboard - remove RAM from that slot, and the system booted fine with RAM in the other slot only. (Of course I had been storing the board for long enough that it was out of warranty, but that's another story...) I suspected a bad solder joint or tin whisker somewhere on the bad RAM slot, but my soldering iron was misplaced a while ago, and a visual inspection of the underside of the board looked OK.
I have been testing more boards than I used to over the past year, and I have found a number of other boards which have bad RAM slots, so I was wondering how many bad RAM slots others here have run into on otherwise good motherboards.
Also, has anyone ever successfully fixed a bad RAM slot, say with a solder reflow?
So far, in terms of failure modes with bad RAM slots, either any RAM in that slot is not recognized and ignored, or else the system won't boot with any RAM in that slot, either locking up during POST or black screen before POST, sometimes with beeps. Any time I have had memtest rack up errors, I have eventually traced it to an actual bad stick of RAM, but has anyone else noticed bad RAM slots causing other symptoms?
On dual processor Xeon boards I have further findings:

• If the blue (primary) RAM slot in a channel is bad, that whole channel is unusable
• If the first blue slot for a CPU is bad, that CPU socket is unusable
• If a non-blue slot is bad, usually only that slot is bad

Old Motherboard Slots

Does anyone else have any experiences to add?