apparently some have already noticed the bug 4.26.2 with the FPS drops to over 50%.
I searched forever what it is and had found that it is due to RHI DX11 / DX12.
My game had an average of 120FPS, now at version 4.26 only 30 to 50FPS.
With an empty project the FPS collapse, now set Windows DX12 the FPS go up. If you set DX11, the FPS drop.
Now you have the problem that this also affects shipping and players with old systems the game crashes after some time.
Switching to DX12 only helps until you quit your editor. If you now start your editor, the FPS collapses even with DX12. If you click on DX11 and then on DX12 again, everything is fine again. But if you now pack your game with DX12, you have microstutters in the game.
Is there any news in this regard yet?