Framerate randomly rising and dropping

[I_Create_Art]

Hi all, so I have a very large scene I’ve worked on for 3 months now and since yesterday my frame rate started randomly rising and dropping, previous it ran at an average of 58-63 fps but now it’s randomly switching between 18-22 fps and 58-63 fps. the fps stays low for about 2mins, then high for 2mins, the low again. I tried to use the gpu profiler to trace the problem and I’ve noticed that under prepass ddm_allopeque (forced by dbuffer) “Masked” is chewing up a huge amount of mms when the fps is low. This is occurring randomly, even when there’s nothing onscreen but the sky. I’ve tried to check my cpu & gpu temperatures, both checkout fine. Just a note, before yesterday I built lighting (it took 45hours) and everything seemed fine but I only spent a few minutes checking the scene, that may have something to do with it but I’ve built lighting many times and this never happened before. And sometimes I do get TEXTURE STREAMING POOL OVER 300.5 mb but I guess this is due to the 4k textures.

I actually just completed this projected yesterday, or I thought I did so for this to start happening now is particularly frustrating. Could anyone help me figure out how to solve the problem, thanks in advance.

Here’s are some screenshots from my profiler.

[Low fps][1]

[High fps][3]

Some specs from my scene,

total number of objects: 4102 (masked objects - 65 trees, 400 grass patches)

average texture size:4096x4096

average masked texure size: 2048x2048

average lightmap size: 128x128 - 256x256

Built lighting:yes

Exponential height fog with Volumetric fog: yes

Dynamic lighting: no

Hardware specs,
cpu: i3 2120 (this is a bit weak)
gpu: radeon r9-380 (4gb)
ram: 16gb
ssd: 256gb (lots of freespace)

[I_Create_Art]

Update: I reduce the resolution of my masked textures by half and in its low state the fps improved from around 18fps to around 34fps, so it definitely has something to do the masked objects. But I’m still not getting a constant 58fps+ like it was 2 days ago, and still don’t have a clue why this is happening now cause there’s been no significant change in my scene besides rebuilding the lighting and that has never caused problems in the past.

[I_Create_Art]

Don’t know why but at least I now know whats causing the problem now, I usually increase the texture streaming pool size whenever I load the level to get the textures to display properly, since they are 4k they need a lot of memory but this seems to now be causing the fps to randomly drop. I ran the level for a few hours without doing this and there was no fps drop.