Basically, a weird light speck tears through mesh every 10 or so frames of rendered material. Random, unphased by my bias settings (I was first having these issues with my emissive material + volumetrics, switched out for a simpler setup - everything in the file). Bias, glossy clamp, bloom or no bloom - it still happens. I have no idea why.
Sorry but I really can't figure out what's happening - I've replicated a problem I was having in a project I'm working on, and I'm attaching a .blend file here.
I'm working in 3.0.0, but I just tried this in 2.93 - same deal. To reproduce you'd better render the animation, since it's a random thing and doesn't always happen.
Not tried this in Cycles, since it's of no use to me - I'd die before I render the needed stuff (I ran the numbers and it's 10 days of rendering). Here's hoping CyclesX comes out soon.
UPD: I have found this question: Blender Eevee lighting Rendering - Flashes of light in animation While it is probably the same issue as mine, people there focus on bloom, which, as I said, is not the culprit. There is a good suggestion there to re-render the faulty frames, but since I'm planning to do 5-6 min of animation, this could mean a ton of unnecessary work over something that shouldn't happen in the first place IMO.
I am considering rendering in some weird 66 FPS setting so that I may delete extra frames alongside faulty ones, but that's not ideal either, albeit less time-consuming.
Rendering the thing without volumetric lighting on didn't help. It still happens.
https://developer.blender.org/T77202 Apparently, this might be an NVIDIA driver bug. Welp. I will try to update it. Will keep you guys posted! This question is like my personal TODO page now.