Yeah, I agree. I'm still wondering what the stuffed in that AGESA update because both boards I had would no longer work with any memory speed over 2133 once I flashed it. Currently clocking my previously 3200/C15 kit at 2133/C10 until the next update rolls out.
Different AGESA code has a huge impact on memory compatibility. It seems like GIGABYTE and other companies would go with the broadest compatibility, but I'm guessing it comes at some sort of cost our you'd see BIOS versions like F5g. I've never seen a whole lot of information on what these UEFI versions do outside of memory compatibility. So far, F5g has the broadest memory compatibility I've seen. Even then, I've had trouble getting AM4 to run stable speeds over DDR4 2400MHz. I think Kyle's only had success with one specific memory kit. Between the two of us we've got at least a dozen different kits to choose from that simply don't work right with the AM4 motherboards we've tested. Many modules rated for nearly twice JEDEC speeds won't even allow the system to POST at DDR4 2666MHz. In one case, I get a no memory beep simply by changing the memory clocks from DDR4 2400MHz to DDR4 2666MHz.
It's a ridiculous situation. I thought that the poor XMP compatibility exhibited since X99's launch was bad. This shit is nothing short of unacceptable. I'm no stranger to the issues that often result from being an early adopter but AM4 memory compatibility problems are unreal.