I just updated to 5.4.1, and everything was smooth when I opened the project. However, after about 5 minutes, when I switched to another application and then back to UE, the issue occurred again. I checked the logs and found three identical lines of warning, all saying “LogD3D12RHI: Display: Temp texture streaming buffer not large enough, needed 8388608 bytes”. So, I tried to find where to adjust this buffer. However, I’m not familiar with the editor settings, so it took me some time and I still couldn’t find where to make the changes. But magically, after searching for a while, the severe lagging issue was suddenly resolved. However, when I switched back to the Chrome browser and then back to UE again, the severe lagging issue reappeared. I’m not sure if this is related to UE’s power-saving mode while running in the background.