Sounds like your cpu imc is the issue. Like I said the motherboard only tells your hardware what to run at. It's not the final determining factor. That will come down to ram hardware specs & cpu imc willingness. Sounds like it may be time to check your cpu/ram in another known good working pc.

Resetting the cmos, or resetting to factory optimized defaults should clear anything that might have gotten set wrong. I don’t think your bios is corrupt, but you could try reflashing if you want. Your board does have a multiple bios switch, so you don't even have to reflash, just try another bios by flipping the switch.

Nereus
Did that of course. Just reflashed bios to make sure, but same issue.. yet all the ram works fine in another rig. Why would this rig suddenly stop being able to post multiple sets of ram unless they are set at 2133MHz?

I’m thinking because the cpu imc is going bad. But you think it’s the motherboard. That is why I suggested testing your cpu/ram in another rig in an earlier post.

Sajin

Nereus
Did that of course. Just reflashed bios to make sure, but same issue.. yet all the ram works fine in another rig. Why would this rig suddenly stop being able to post multiple sets of ram unless they are set at 2133MHz?

I’m thinking because the cpu imc is going bad. But you think it’s the motherboard. That is why I suggested testing your cpu/ram in another rig in an earlier post.

All the ram is fine in another board, could be the CPU imc but the CPU was fine in the Z590 FTW before I got the Z590 Dark, and was fine in the Z590 Dark until just recently. BUT WAIT! The weirdness continues...
 
I don't know why I didn't do it sooner, but I tried running with just one stick in the DIMM1 slot only (the Z590 Dark only has 2 DIMM slots). I tested with all 4 sticks, one at a time (2x16GB @ 4000MHZ, 2x16GB @ 4800MHz). Having only one stick in DIMM1, all of them posted with XMP settings straight away with no issue. This seems to indicate that DIMM2 slot has an issue right? Except after testing all those sticks individually, and then running with the 4800MHz at XMP in DIMM1, I then installed the other 4800MHz stick just to confirm the issue was that DIMM2 slot... but now it posts at 4800MHz XMP with both sticks again! What the hell is going on? lol.. maybe some intermittent issue, a poor solder somewhere perhaps? Really really weird. Maybe when it heats up enough, the connection on DIMM2 slot fails? That could explain it.. maybe. 
 
So bizarre. Would a failing CPU imc impact only 1 DIMM slot and not the other? Seems unlikely, but I don't know the architecture...
 
Once I have the Z490 Dark back (and confirmed it's all working), I'll look at RMA'ing this Z590 Dark. It needs to anyway because of the post code LED not working, but wow.. bit of a head scratcher. CPU failing is really rare (other than burning it out with insane overclocks) - I've never had a CPU fail so I'm inclined to think it's the motherboard at this point. If I didn't have a full water loop, I'd just swap to the Z590 FTW and confirm it. Sigh..
 
edit: Intel have a diagnostic tool (link), I'll run that and see if the imc test fails.
 
Intel diagnostic test - imc passed. Neat tool, really puts some stress on the CPU - I had one core hit 72C on default clock on water, highest I've seen the temp on this CPU. Anyway, that points more toward the motherboard too.
 

 
 

Sajin
The reason everything worked is because you put less stress on the imc by running a single stick. Each stick adds more stress to the imc. Looks like your imc can handle single stick at higher speeds, but not dual at higher speeds anymore. Still looking like an imc issue to me.

Note: xmp is overclocking.

Yeah, but then they did start working again - both sticks at 4800MHz. Also the CPU passed the Intel diagnostic test for the IMC. Now I'm back to only 1 stick again after trying the 4000MHz sticks. It sure feels like there's something wrong with the DIMM2 slot with it working intermittently. I will put a ticket in and see if EVGA have any other suggestions before I pull down the rig and RMA the board. If I get the time, I will rebuild with the Z590 FTW board.. if that has no problems, then I can rule out the CPU imc.
 

underclocking my card seems to work. it was at the stock clock so this has me concerned. hopefully BF2042 doesn't become one of those games that are killing GPUs
 

SnapScorpion
underclocking my card seems to work. it was at the stock clock so this has me concerned. hopefully BF2042 doesn't become one of those games that are killing GPUs
 

It's a known issue and downclocking your GPU 25-50 is one of the 'fixes' for the time being. 
 
I had to do the same at stock settings and set it at -50 but have since bumped it to -25 and it still runs without crashing.  

Hope they figure this one out.
 
Edit: I literally just jinxed myself. LOL!  I'm going back to -50. lmao
 

Kuro1n
I am getting the same error you have 3080 Ti, all low BF2042 and underclocked/volted. :(

I tested it under both,  win 11 makes 2042 crash alot more for me than in Win-10
Which are you using?   

My 1080 Ti going strong!

Unfortunately the issue has resurfaced again for me. This time it doesn't even give me the courtesy of an error message, disappearing as soon as a match is finished loading and when the 3D stuff is ready to start rendering. 

EShew
BF 2042 is EXTREMELY buggy. Expect issues for another 6 months at best. 

 
Well this statement aged accurately.