Huge weird performance issues

Hi,
The last few days have been really weird and I have no idea whats been going on.
So I tried importing a megascans rock asset and the high LOD took forever. it was nearly 1 million polys. The material editor would crash the whole engine when i opened the corresponding imported material. At first I thought it crashed so I shut it down through task manager. did this a bunch of times. then i realised i was just being impatient. I left it on while I looked through the saved logs and it just happened to work. Next i reimported it with all the LOD’s and it just atleast 30 mins.
Since this the engine has been extremely weird. It started to perform really badly. For example the HZB setup 512*256 or somethig similar to that took 40ms. then it kept to 8 - 10ms. This was on a simple mimal default level where i deleted the sky sphere, the lights and reflection captures. I was trying to learn lighting and put in a point light with a large attenuation radius and 5000 intensity. When playing it would slow down the above stat. but the funny thing is sometimes it would be fine for a bit. Later I read about this and saw issues about slateUI which was an issue for VR, however this manifested itself in my third person project. No VR. I thought it was an issue with drivers and checked and then thought it might have been a windows KB update that for some reason wouldnt allow an uninstall of itself. I used system restore and that didnt work. I reinstalled the engine and the windows update installed itself to.
I also tried loading a demo level from a content pack (desert town) and this ran around 20 frames. Even worse is that the first time i opened the level it took around 30 mins to open and then crashed around 90%. I tried again and still it took forever but this time opened. I then removed a second TV I had hooked up to my GPU for a better workflow. For some reason its now working better but still dropping to 70-90 frames for some reason. I put it back on and its still the same. Working but still dropping to 70-90 frames. Also Desert town scene now opens in around 15 seconds.
Somebody HELP!!!
have i broken my engine. i reinstalled the launcher and engine and it wasnt working, then it was so im worried its gonna happen again. I dont know what the hell is going on.

It probably won’t help but make sure to clear up space. Detailed objects with high res-textures often seemed to take up a lot of memory and after I deleted the Derived Data Cache (and maybe “Saved” and “Intermediate” too) it ran faster again. (Make sure to do a backup first, especially if you’ve been using plugins.)

Hey, thanks for your reply.
I will definitely try this. Also is there anything i need to be cautious about deleting those folders. I came across this as a fix for some other issue awhile ago and read it was dangerous.
I believe i have one object, a rock with a 8k texture from megascans, but this is surrounded by trees from speedtree. Would this even have any input to the gpu when its completely out of view.
I have installed the substance, input buffer basic and aes targeting plugins. I havent actually done anything with them yet so they shouldnt cause an issue.I’ll let you know how it works put

Unfortunately it didnt work. I deleted saved and intermediate folders in my project folder, appdata local folder for both epic launcher and the engine.
Took a while for the engine to load my level but that was expected.
Also its HZB setupmips 1 9 that takes 20ms.

Oh, unfortunately I can’t help you any further with this since I don’t have enough experience with similar cases. I really hope someone with more experience can help you with this issue! Did you try reinstalling your engine?

thanks for trying anyways. i think i figured something out. its not the best bust it works for normal PIE.

so i set r.HZBOcclusion=0 in the console variables and stopped using a new PIE. I now use just the standard play in viewport which takes hzb setup mips to 0.04ms. If i use the separate viewport window it now reduces framerate to around 70-80. This is from setup mips and from slateUI. slateUI is probably beause two windows are being rendered.
If I use standalone where the map is saved and opens a window(i believe this is closest to packaged for playtesting) it reduces to 62 fps but this is consistent so for now it seems to be okay. its not ideal but i can stick to the play in viewport mode for now.
Its just weird that this started after id been using separate viewport for testing for awhile. could be caused by my foliage but since its working fine for now im not gonna risk it.
All that said it might just mess up again after i post this lol.