Hello and welcome! You happen to have the same setup as my “Guinea pig”, namely ZX-99EV3 v1.23 and 2620V3. So I can fullly answer you based on my own experiences:
- What RAM slots are you populating? I assume next to the 8-pin CPU power connector, and not by the 24-pin power connector?
- The lowest JEDEC speed for DDR4 is 2133. Dropping the speed down to 1400 seems crazy low. So I would start with hardware cleaning as described in this post. But you have to be open to the idea that one of your sticks is broken. And now is a very bad time for buying RAM.
- Next, you can indeed put a much, much better BIOS on the board. RAM voltage adjustment does not work however (very few Chinese X99 boards can do this). And in its default configuration, you need a GPU with UEFI support. Just follow the instructions in this post and put together a “D1_M2_B2” BIOS.
- Lastly, you happen to have the best hardware revision of that board. If you want to, you can connect a TPM 2.0 module on the Debug port