I've been doing some visdev for a project of mine, which has involved me constantly adding to a single scene.
I returned from an outing and completed work on a particular object, then went to render it in the test scene- here, Blender suddenly takes a huge amount of processing power and time to render the scene.
The only things that changed between this occurrence and the previous render (which completed very quickly with absolutely no issues) were the addition of several new materials (slightly altered copies of an older one), the creation of a copy of the object I had finished, and adjustments to that object's particle system- nothing you would think would mess anything up.
Now here's where it gets strange:
If I open up an Autosave of this scene from a time when the renders worked out perfectly, the renders take forever- just like the current instance.
If I take the current version of the scene and remove everything I had added between the last successful render and the issue starting, the issue persists.
And if I delete everything in the scene, save the camera, it works perfectly again.
Mind you, there have been no changes to the Compositor, the system or background settings in the scene, the shaders, or anything technical, nor have there been any updates or hardware changes to the computer, itself.
I'm very confused.
The scene has a lot of particles- did my computer suddenly get tired of rendering them after spending several days doing just fine?
It's not like the new object's particles were the straw that broke the camel's back in regards to the particle limit, since going back doesn't fix it, and if I only delete the most particle-heavy systems in the scene, the issues persist.