Crashing On PReviously OK File, CUDA error?

Went for lunch, saved my file. came back, opened it, started adding another material. when i went to Rendered view, Blender quit. I can’t find the crash log, can someone point me at it? Currently on 2.82.
After that i reloaded the autosave from before lunch, seemed ok but when i hit Rendered View it said “Cancel” at the top of the screen. When i F12, i get “Cuda erro at cuCtxCreate. Launch failed”.
any ideas what’s suddenly happened?

EDIT. Bit more info, seems to be very hit and mis as to throwing these errors. managed to get a console window up, says
"CUDA error: Launch failed in cuCtxSynchronize(), line 1835

Refer to the Cycles GPU rendering documentation for possible solutions:
https://docs.blender.org/manual/en/latest/render/cycles/gpu_rendering.html

CUDA error: Launch failed in cuCtxSynchronize(), line 2309"
that link doesn’t say anything useful.

TIA

Most of the time it means the GPU cant handle something, VRAM wise (it says CUDA, but I have seen this error many times). By example, you said you add a material. Maybe a recent too heavy image causing the problem. And it can happen very fast, check the files you are using for your materials or if you have volumetrics, any thing you added to the scene. It can happen to any GPU. Edit: if you get the error, you must close BLENDER and reopen it to make it work again, no matter what you do.

Event log’s saying TDR detected, code 7. Dunno why it’s having a problem, it was literally the same file but w/ one new material i test-allocated to about a dozen faces.

Try to remove that material just to check, even if allocated to 1 face.

Seems to be when i’m focused on an area using a material that has the Ambient Occlusion node in it. Seemed to be ok when i was creating the material though. going to another part of the model and using Rendered View is no problem.
i’ve not used the AO node, just came across it in a YT vid and it looked like a good effect that i wanted, is there any tricks to usuing it, recommended settings etc? is it known to be resource-intensive?

TDR is a known problem, what can happens sometimes, if the calculations for the grafikcard needs to long time.