Render time unstable

I tried to render an animation. The first image takes 1 minute.
The 2nd image takes 4 minutes, and nothing special has changed between the 2.
Any idea of what could cause this ?
Thanks !

What kind of animation?,motionblur,deformer eevee-cycles?,
only camera then if you use 2.93.x
(cycles only)try persistant-data.

Thanks for your answer.
Sorry. I should have given these infoz !
Well : Cycles, on 2.93.2, and yes : motion blur.
What do you mean by " only camera" ?

Alas, Persistant-data changed nothing …

Well, it seems that 3 Boolean modifiers caused this problem. Once removed, everything is back to normal …
These guys are dangerous.

Note that after removing one of these 3 Booleans, 3 images get rendered normally, and then the 4th is ultra slow.
Isn’t this a problem of memory saturation ? …

I don’t know how Blender uses memory for such actions.
The geometry is probably high resolution?
By camera I really only mean that the camera moves through the scene, everything else is fixed.

Maybe you can optimize/cache the booleans
with the mesh-sequence-modifier.

A gaussian modifier is also involved in the mess. so I think, you’re right.
I tried to export the animated object to .MDD but the Booleans produce objects with varying number of vertice : no import is possible.
I try with alembic …

Export to Alembic … and then import.
It certainly looks like a waste of time.
Moreover I couldn’t find a way to export only one object to alembic. So I have to create a dedicated file only for the moving mesh ( the one with plenty of sick modifiers … )
Any way :
Thank you Walt !!! :v: :+1:

Well, please.
Sometimes we are still very far away from realtime rendering.
Have you tried cxcles X?!

Not yet, I thought that it was included in B3 … I installed it but no …
I haven’t figured out how to try it (for free ) …
Waiting for October !